It was certainly a penalty. But it should not have been called.
The whistles were put away for most of the 3rd period, so many calls were let go. And to be fair the Bruins got away with more, but you don't call a penalty with 2min left in a tied hockey game when you let everything else slide.
As a leafs fan I'm happy with the result. As a hockey fan it was a terrible way to end the game.