Well, that's the thing, it's a contact sport and Kuminga just acted that way because he felt like the contact was too much. Frustration really does things and sometimes it gets out of hand.
It was a good foul made by Jordan Clarkson and the refs just romanticized it and it's all good not until Kuminga probably said something that made JC in total rage. I'm not sure what he said but it seems that those words flamed JC and made him react that way, maybe as an insult or what.
Anyway, it's great revenge being done by the whole Jazz against Kuminga. They've won in the last few seconds of the game, JC's smiling for sure in the locker.
I think it was not a good foul, he was behind Kuminga and still tried to get the ball, so at that angle, it was a clear foul, he was only penalized for Flagrant foul 2 because he showed his fist as if he is ready to fight. I understand that frustration but he has to realize that to win, being cool is always the best thing to do. For the refs, the actions are more visible than the words, so that alone I'm sure he knows that already.