Anyone who has watched the game or even the highlights can easily see that Kawhi did not foul Harden, not even close, not even remotely explainable, and you know what's worse? They actually reviewed it, because it was challenged, and they still stick with the call instead of changing it because changing it would mean that they made a bad decision to begin with and they can't accept that so almost all obvious calls that gets challenged usually stays the same.
IIRC, they didn't review it.
Clippers is out of challenge at that moment but that's under 2 minutes so it can be reviewed but refuse to.
I think it was the view of the referee that made it a wrong decision.
He's view was at the back of Harden and didn't see the arm clinging to Kawhi which is why he tried to take it off with a little push.
That's a reaction of someone being grabbed while going to the rim.
This happens a lot unlike before. i.e. 80's and 90's
I guess we will just have to live with that and maybe they could find a new rule to go against it.
Some suggest to give one more challenge in case the first one was successful.