Impending others evacuating can be alleviated by giving him a window seat.
Practically - true. But there's still a requirement (in our books at least, which reflect the legislation changes over recent years and have certainly been "lawyered") that if a passenger is not able to find an emergency exit unassisted they are regarded as not being self reliant and must have a travelling companion.
Maybe with this chap being alledgedly partially sighted he's managed (as many do) over the years but it does seem he needed assistance to the aircraft door on the flight in question and maybe that's why he rang bells with the crew on this flight, it then (legally) becomes a decision call for the PIC.