He initially had an empty seat next to him on Flight 901, but a late passenger sat there and took more space than he paid for.
That meant that, though he did manage to wedge himself into his seat for the takeoff and landing, he was unable to comply with the requirement that his seat belt be fastened at those times
Dreamland it seems that the cc didn't do their job properly when they didn't ensure that his seatbelt was fastened.