Argentina coach Daniel Hourcade insists he, nor his support team, saw the incident but it left Cheika bemused.
"No one (from the Argentina team) was injured, and Nick's probably trying to get ball - I'm really not sure what is going through anyone's mind to be honest," Cheika said.
"I think the ref dealt with it on the field, in the way he thought was best.
"I wasn't quite sure about the penalty."
Cheika said it was a rarity to see such actions on the field, but pointed out that assistant coach Nathan Grey copped a push mid-match by England's fullback during the mid-year Tests when a ball had been kicked into touch.
"It happens once in a blue moon. It's not something that anyone needs to prepare for," Cheika said.
"It shouldn't happen. That's just the way it was. He (the medic) was out there, the ball went out to him and he got in the way."