Being on the flight I was in 5A and passenger in 40c I could not tell if the gentleman needed a seatbelt extender but if I had to bet I'd put my money on yes.
I also couldn't tell if there were people seated next to him in A or B but considering the flight was full I would also put my money on yes.
I also know that if there was an emergency A and B would have a hard time getting by him.
Was the man flying alone can't say but if he wasn't no one in his party assisted in his boarding, as for deboarding no clue I was excited we hit b20 and didn't have to do a 5 mile walk to customs so I ran out.
Now I know there are ADA regulations and ACCA I am 100% sure I do not know them all nor will I pretend too. But I honestly think in a case like this and for the safety of the passenger, he shouldn't have been on that flight. The look of pain on his face as he stood at the plane door, and then as he was being supported by the airport employee by seat 1D was heartbreaking.