You are right, but somehow that ruling seems like it needs to be changed. I don't know how, but that was a fumble. The receiver even took a step and a half to progress after the "catch" before he was smacked.
Not unless we want the Supreme Court involved. Once the whistle blows, you can't undo the call because you have no idea what would have happened next.
Look. players drop passes, miss blocks, fumble the ball, forget the snap count etc. Sometimes the officials blow it too. It's part of the game. Demanding that somehow every wrong be made right in football is as silly as thinking that our litigious legal system can make every wrong right. It can never happen.