Unpopular opinion forthcoming: The closer I look at that play, I think it may have actually been a foul on Splitter. TNT should have shown more than this one angle but it's an offensive foul if you dislodge a player's armbar. It's difficult to tell from this angle but it looks like Splitter's swipe with his off-arm dislodged it.
It's not a call you see much when it's big vs. big but it's technically the right call. And really it's even more reason why Splitter went about posting up Fisher all wrong. If he catches the ball that far out, the right play is to pass it back out, fight for lower position and then go straight into a shot. If you post up a point guard 12 feet away from the basket, you're going to be called for an offensive foul 75% of the time.