"And even though it's not going to bring Chelsea back, for me, for this company to be convicted, I think it's a good outcome."
He added it meant the company won't "walk [away] scott free".
Earlier this month the company admitted a raft of failings over its quad bike safari in which Ms Callaghan died, including defective and poorly maintained quadbikes, inadequate safety helmets, and a lack of supervision or an emergency plan -- factors Mr Callaghan today described as "dreadful".
"Unfortunately it takes a tragedy to bring them to account," he said.
Riverland Adventures argued it should not be charged under workplace health and safety laws because the crash took place on a public road, and therefore did not constitute the company's 'place of work'.
In a judgement released to APNZ today, Judge Charles Blackie ruled that argument invalid, and said the company, "regardless of the fact it is now in liquidation, will be convicted".
"If the defence argument in this case were to be upheld, it would mean that any company or enterprise operating a business such as Riverland Adventure Tours would be liable for the consequences created by any hazard while the hazard remained on the property they occupy, but would be totally free from liability as soon as they drove out of their front gate and onto a public road, transporting with them and continuing to utilise the same hazard or hazardous situation," he said.
"That cannot be the law. It would mean the tour operators who provide defective vehicles, gear and equipment could do so within impunity, provided they operated on a public road or over an area in respect of which they had no direct control."
Judge Blackie said "there is no doubt" that Riverland Adventures had an obligation to ensure its quad bikes were safe and fit for purpose.
"In the case of the quad bike ridden by Ms Callaghan, it was not," he concluded.
Mr Callaghan said despite the fact the tour operator will be unlikely to pay any fine which might be imposed at sentencing, he was "just pleased they've been held to account".
"At least they'll hold a conviction, that's a pretty big thing."
A sentencing date for the company has yet to be set.