Retallick upended Hanigan as they were getting to their feet following a tackle in the first half, prompting an angry outburst from Wallabies coach Michael Cheika after referee Nigel Owens let the incident go unpunished.
Hansen said there was no intent from Retallick.
"When somebody jumps on top of you, you get up on your knees and he falls off, it's an accident," he told reporters in Dunedin on Sunday. "It's not a deliberate act."
Owens and television official Rowan Kitt reviewed footage of the incident and both said at the time they believed the players had just been clumsy in getting to their feet.
Cheika, however, said after the All Blacks' nail-biting 35-29 win that the incident was clear cut and Retallick had "categorically" picked up Hanigan and dumped him on his head.
"I don't want to get into that," Hansen added. "(Cheika) made his point and that's fine."
The incident has echoes of a similar dispute last year when the Wallabies coach accused Owen Franks of eye-gouging Kane Douglas during the clash in Wellington.
Southern hemisphere rugby's governing body SANZAAR reviewed the Franks incident and said there was no case to answer.
Hansen said he felt the Retallick incident was exactly the same.
The All Blacks coach added he had few injury concerns as they head into the week off, but tighthead prop Franks, who was ruled out of the Dunedin test, will likely miss the remainder of the Rugby Championship after sustaining an Achilles injury.
"I think we are aiming, if we do get him back, for the end of year tour," Hansen said. "But we won't risk it. He is an older athlete, got a lot of miles on the clock.
"If we want to get him to the World Cup we just have to do things right with him."
Centre Ryan Crotty and flanker Sam Cane, who failed head injury assessments, would also be monitored ahead of the All Blacks' next match against Argentina in New Plymouth on Sept. 9.