He did give them a key after all.

Wow, I didn't know when I gave my neighbors a key to my house to keep an eye on it when I was on vacation, that I was also giving them carte blanche to come in, clean, do home improvement projects, and go thru my personal belongings and throw them out if they wanted.

There must be poor communication between these parents and their son.

Or the parents are overbearing control freaks who still think that their son's home = his room in their house over which he had no rights.