He reached in unnecessarily and got called...
I just went back and rewatched it multiple times, at full speed and slow motion.
The ball went into Omoruyi, who held it over his head and was defended by Hawkins. Harris came over and doubled, hitting Omoruyi on the arm and in the face with no call. Hawkins knocked the ball loose, and both Harris and Omoruyi tried to get it - it was at this point where it looked like Omoruyi may have hit Harris in the hand while going for the ball.
The ref was right there and watched passively, making no motion and no call on that contact. That was the only thing that could have been considered a "reach" - and it wasn't called. So, it was NOT a reach-in foul.
The ball bounced toward the sideline and both Harris and Omoruyi went after it. Harris got to it first, and Omoruyi stopped and put both hands in the air, his hip/thigh coming into contact with Harris' shoulder as Harris corralled the ball. Again, no call/movement by the ref, who has been clearly in frame of the camera the entire time.
Harris then started his dribble into Omoruyi's hip and puts his forearm on Omoruyi's body, who was not moving and had both hands over his head. Omoruyi realized he no longer had a play on the ball, and turned to run up court.
THIS is when the ref called the foul, just as he slipped out of frame.
So, not a reach in foul at all. The only thing I can think of that the ref may have called was that Omoruyi fouled Harris with his body, but Omoruyi was immobile at that point and Harris initiated the contact.
Omoruyi was understandably confused at the whistle, turning around as he got to half court wondering what had happened.
I'm sure you have it on DVR and can go back and watch it yourself. Omoruyi got the ball at 13:59 and the foul was called at 13:55.