You're right that it made no difference, but by the Laws of the Game, he had to do it.
All the refs at League level will have assessors in the crowd, so they do have to follow the Law to the letter, which, in cases like this, is stupid.
Also, the advantage rule doesn't come into it at all, a drop ball was the correct restart, and the only one he could have given, regardless of it being over-officious.