"It would be one in many thousands of chances that would happen," he said.
"There might be a variety of ways. One is just a straight error, that the lab called it wrong. Another might be that they are dealing with tiny quantities of the sample, which are perhaps indifferent quantities within different parts of the sample.
"There are a few different ways it could happen but I don't know what might have occurred in this case."
The original A-sample was tested at the WADA-accredited laboratory Sports Medicine Research and Testing Laboratory (SMRTL) in Salt Lake City.
Tuipulotu initially left the All Blacks squad on the eve of the side's final test against France in Paris last November for 'personal reasons'.
The 24-year-old was adamant that he had not deliberately or knowingly taken a banned substance and nor was he aware of any product that he could have inadvertently consumed that would result in him testing positive.
Still, having failed a test, he was left in limbo until yesterday when the results of the B-sample were announced.
Steel said the delay to proceedings was 'quite extraordinary'.
"In my mind it's quite extraordinary. If you're an athlete and you really are surprised by what the A-sample shows, I would have thought it's in everybody's interest to get the B-sample tested as soon as possible. And that's the normal case it would have been tested within a couple of weeks so delaying it really gives the opportunity for this saga to drag out. This thing I would have thought could have been cleared up in a couple of weeks," Steel said.
"None of this information should have seen the light of day. There is no question around Patrick and his integrity as an athlete but the delay in all of this seems to have allowed it to leak and so Patrick's been questioned when he shouldn't be."
The difference between an A sample and a B sample
"They are taken at the same time," Steel explains.
"You get a single beaker from an athlete that is divided into two different bottles and sealed at the same time. One is taken away and analysed while the other is frozen. If the A is positive then the B can be analysed if the athlete chooses. So they are taken from the same cup, just divided into different bottles.
"The B's the failsafe if you like. It's the athlete's opportunity to double check the A sample."
Timeline
Mid November
Patrick Tuipulotu takes a drug test in the lead-up to the All Blacks final test against France.
November 21
He leaves the All Blacks' camp due to 'personal reasons'.
February 5
New Zealand Rugby confirm Tuipulotu tested positive to drugs test in November and was provisionally suspended.
February 9
Tuipulotu cleared after B sample produces negative result.
