It looks to me that he didn't book special on-board assistance or he did book it but was told wheelchair was not available on that particular type of plane, was offered rebooking/free cancellation, but decided to fly anyway. That would be perfectly OK- I'm guessing he's from London so it's a 2.5h flight -most people never use toilets on such short flights
In addition to that, if he can't lift himself/reach emergency exit on his own, he should have travelled with a companion to help him. Where was his companion? Flight crew do not provide that sort of assistance. On most, if not all airlines, they won't even help you lift your bags, let alone help you to the toilets.
Basically I have a slight impression that he did it on purpose, for the drama and attention. He is a reporter after all. Always on the look out for things to report on and be outraged about.