He played the odds and lost this time.
This flight was fully booked so he had no empty seats to occupy....................
And the clear implication is that had there been an empty seat for him to sit in upon exiting said lavatories, he would have gotten away with it. Unless the young girls double scanned boarding pass had prompted a full seach of the fully occupied plane and a demand to see and verify photo id’s of all aboard; doubtful.