The incident occurred during a scrum at the midway mark of the third period. Toronto was leading the game 5-0 at the time, when Montreal forward Brandon Prust attempted a hit on Grabovski, which prompted the scrum. Pacioretty grabbed Grabovski from behind while he was engaging with Prust. Pacioretty's arm comes across Grabovski's face with his hand grasping the side of the Toronto forward's helmet. He clearly was covering Grabovski's mouth and emerged from the altercation with his hand on display as if something had happened.
At the time, it was difficult to determine if he had been bit.
Thanks to Grabovski's admission, it's clear what occurred, via Puck Daddy:
"He was choking me and I bit him. Don't stick your hands where you shouldn't. To be honest with you he was choking me pretty hard, to the point where I really couldn't breathe. And I couldn't pull his hand away at all. I tried to hit him with my other hand, but I couldn't because he was choking me. There was nothing left to do but bite him."
Interestingly enough, Grabovski was asked to hold a phone hearing with the NHL Department of Player Safety after the incident. Player Safety ruled that they couldn't accurately determine what occurred on the play. This means they likely asked Grabovski directly if he bit Pacioretty. Considering he wasn't disciplined because they couldn't conclusively determine what happened, one would imagine that Grabovski told Player Safety that he did not bite Pacioretty.
Meaning, he lied.
Whether the league takes any kind of action following this development remains to be seen. However, if Grabovski faces discipline in the future, this incident could resurface in the collective mind of Brendan Shanahan's department.