In other words, Key had infringed the delicate protocols which limit how far politicians should go and decree what is best left for officials.
Rennie's arcane language may have been lost on many - but not on the ninth floor of the Beehive. It was about as close as the country's most senior civil servant could come to reprimanding Key for overstepping the mark between acceptable assistance and political interference.
Only gently, of course. That is because, as any good public servant also knows, the minister - especially the prime minister - is always right, even when clearly in the wrong.
Rennie has had his detractors - including this writer - during his five-year term as commissioner. But on Thursday he rose to the occasion in decisive, yet strictly non-partisan fashion.
His intervention was in contrast to the prime minister's office whose idea of damage control was simply to tough things out amid a media feeding-frenzy of almost biblical proportions.
Rennie spent some time explaining that unlike the appointment of most chief executives, where the relevant minister has only the right to veto the State Services Commissioner's final recommendation, the position of director of the GCSB is one of a handful of statutory officers where the appointment process allows the minister far more say. Key thus had more leeway than his attackers were giving him.
Rennie expressed "disappointment" - another heavily loaded word - with the misinformed criticisms levelled by a former boss of the GCSB, Sir Bruce Ferguson. Rennie rubbished the notion that the job required a background in the military or the intelligence community.
He indicated that even before last year's mega embarrassment over the surveillance of Kim Dotcom, it had been realised that the spy agency was in desperate need of someone able to restructure and modernise it.
Most crucially, however, Rennie drew something of a line in the sand that prime ministers should not stray across, even unintentionally.
He made it clear Key should have left contacting Fletcher to him. Had Key done so, he would have avoided some of the flak he copped this week. It might not have been practicable, but had Key withdrawn completely from the appointment process after suggesting Fletcher for the job - and left it to Deputy Prime Minister Bill English to make the decision - he would have avoided all of the flak.
The important point here is perception - not just whether Key leaned on the officials, but whether by his actions he was seen as doing so.
Alarm bells would have rung in Rennie's head when he was told of Key's phone call to Fletcher. The commissioner would have redoubled efforts to ensure the integrity of the appointment process, including setting up an appointment panel of absolutely unimpeachable quality which would not be seen to be swayed by Key's actions.
The result would still have been the same. Rennie would have taken the hint. Key would have got the man he wanted for the job. Key would have created sufficient distance from the appointment process to negate Opposition claims he was guilty of political interference.
Key's earlier association with Fletcher instead became a skeleton lurking in the Prime Minister's political closet. Once that association became public, the capacity of both men to be seen to be functioning independently of one another would be compromised.
Given Key's responsibility as the only person with oversight of the GCSB's secret operations, this is especially troubling.
The lid was kept on this unsatisfactory state of affairs until Labour's Grant Robertson struck gold by asking Key in Parliament what role he played in Fletcher s appointment.
Key must have been worried that the question indicated Robertson knew something, so he blurted out that he had known Fletcher, having gone to school with his brother.
But Key did not answer the main question about his role in the appointment. Then again, how could he without ending up with huge egg on face?
Things turned to custard this week anyway when it became known that Key had rung Fletcher about taking the job. Key was deemed guilty by opponents of lying by omission, prompting calls for all manner of official inquiries and breach of parliamentary privilege hearings.
None of those are likely to eventuate. But Key may have stretched credulity too far this time with his claim to have forgotten he made the call to Fletcher. The memory lapse is just too convenient. As a way of ducking questions, it is becoming too frequent.
Robertson sees the lapses as part of what he calls Key's "diminish, divert and demean" modus operandi. Faced with being caught out by some action or statement, Key's response is to diminish the significance of the issue or his role in it, divert attention away from it and, especially in Parliament, demean whoever is raising it.
Robertson's point is that in seeking to preserve his own political capital, Key is devaluing the office of prime minister.
This analysis may have some credence. But Labour's problem is getting anything to stick to Key. While eyebrows might be raised over his bouts of assumed amnesia, Key is unlikely to incur too much lasting damage from this episode.
The procedures of public service recruitment are hardly riveting. Moreover - and this is the truly telling point - if Key has committed a political crime, the public has yet to be convinced there was a truly base motive, such as money, political favour, patronage, or something equally venal.
Key is guilty of cutting corners. He may deserve crucifying for helping a mate - or a mate's mate. But he got nothing else out of it. Finding a job for someone who really did not need his help and who was also more than qualified to do that job does not quite meet most people's definition of real cronyism.
