You know what? I am going to reverse myself on this after seeing this replay:
[yt=]goXD0Q553LE[/yt]
On the initial angle it does not look like a foul, leaving the flail kick as the only basis to make the call. But at the 1:36 mark of the above video they have a nice closeup from a different angle, and would have to agree he got the forearm.
And as an aside -- yes, at the end of the game any and all remote doubts about a foul, all judgements should error 100% on the side of no foul. Its like a death penalty case -- the absolute 100% worst outcome is to have the state (the NBA) wrongly decide to terminate somebody, or worngly decide to give a game to a team that didn't deserve it. If you miss a few fouls along the way, that's fine. That's still decided between the players. Having the refs steal a game by calling a phantom foul would permanently and irrevocably shred whatever is left of the perception of the league's objectivity. Each and every event would be proof of a conspiracy of some sort. You have to be 100% sure. Here on the slowmo reverse angle replay I say that yep, I was wrong, it does look like a foul. I also say, no bigee that the refs missed it -- biggee to the teams and unfortaunte, but obviously very easy to miss at full speed.