You know honestly... I had a different opinion of it.
I don't know if Howard was digging his fingers into KG or not. I don't think it mattered. I think Howard had countless dirty plays throughout the course of the series. He was elbowing people left and right. He pulled Pierce to the ground, pushed Rondo, knocked out Big Baby... and those elbows were clearly dangerous. From Howard's perspective, it is pure intimidation. It tells opponents to be careful trying to defend him. It makes opponents hesitate to battle for rebounds or body up on him. It was working... Towards the end of game 5, our players were playing scared of Dwight. Those elbows were in danger of getting in Boston's head. All the hype leading up to game 6 was that the Celtics needed to send in a Scalabrine to "take out Howard".
Within the first few minutes of game 6, that play happened and I like to think it was intentional. KG is insane. He's one of the most intimidating players in the league. Instead of sending in Scal... KG finds some reason to flip out... and then literally flips out and overreacts. They aren't going to toss KG for it 3 minutes into game 6... and KG had the "handcheck" excuse for his overreaction. But what it actually did was tell Howard, "Look... play dirty and you may have to deal with a mentally deranged psychopath who will tear your skin off". I think KG met mind games with mind games. Message sent. From that point on, Dwight wasn't going to intimidate ANYONE. Game/Series over.
ANd yes... it was a handcheck. And Boston rightfully had a reason to be frustrated with the lack of calls on Dwight leading up to game 6. The NBA purposely fixed games 4 and 5 in order to extend the series and cash in on additional TV time. KG whacking Howard solved 2 things. #1 - Show Dwight that there were potential repercussions for his brand of intimidation and #2 - Overreact to a ref non-call, draw attention to a blatant missed call on Dwight, and make it clear that Boston wasn't going to sit idly by while another game was stolen from them by NBA shenanigans. I can't read lips, but I like to think one of the things KG screamed to the ref was, "Call this game straight... or I'm going to break this kid's elbow... your choice". The fact that no technical was called on KG was telling.
KG is literally about to eat the ref in this picture... and the ref lets it slide. Admission of guilt. They know they fixed those games. In Game 5, they tossed our best defense against Howard with a later recinded technical. They were letting Howard get away with murder up until that point. KG wasn't having it.