Being the PIC on an aircraft with a crew and the PIC relationship to that crew isn't the same as being a supervisor to a subordinate (in terms of improper relationships, sexual harassment, etc.).

He has no influence to ply in terms of promotions, job performance reviews, etc. that would put him in a position of authority he could abuse. When the a/c blocks in and the flight is over, he's just another employee on a layover.