As one of the commentators said after that surprise shot, if he is able to shoot that ball, he will be a hero and it's a different story. It's just that Butler didn't nail it. Many question his action because, before that play, all points made by Jimmy Butler were almost attacking in the paint regardless of how many Celtics are trying to stop him. On that supposed clutch shot, he can attack the rim but choose a game-winning shot. Still, great effort for them to make a rally and almost win the game. They are down by 12 points in the last 3 minutes. What a rally they did.
There are lots of "what if" in that play that's why people should not really question what Butler did.