This is ridiculous. I just don't understand this guy's motivation for causing all this trouble. What's he got to gain?
It's no good saying that if the pilots did nothing wrong then nothing will happen to them because they still have to put up with being investigated and the worry that they might somehow be found guilty. It would also be annoying for them that this guy is able to act in this way towards them despite their doing nothing wrong.
If the facts that have been laid out here are correct, and it appears that they are then he simply does not have a case, ATC permission was asked for and granted, end of story.