One of the refs must have clearly thought it hit the rim, which is why it wasn't a jump ball.
And I recorded the 4th quarter of the game on my computer. I've watched it a dozen times. not including the replays.
There are 3 officials, so in that case you would think 2 of them would have to agree that the ball hit the rim to overturn the call on the court. The official nearest the rim ruled that it did not hit the rim, so it came away from the ball.
The play was so close that it SHOULD have been a jump ball. The probability that one official clearly saw it hit the rim, yet that action managed to evade several replays, is highly unlikely.
You've watched it a dozen times, but you're also highly subject to rater bias. It was in no way an obvious "yes-no" play, which is why even Celtics fans can't agree on what happened.
To definitively say it hit the rim from the replays we all saw would be silly. It's ok to admit that the Celtics were the benefactors of a very close call which appeared to be improperly overturned given the situation. The Magic still failed on several other fronts, which ultimately cost them the game.