I find this whole debate extraordinary!
A 'passenger' was asked to change seats - for safety reasons.
The cabin attendant surely didn't ask this of them to be difficult.
Anyone who's done the job knows that there's little time to action such necessary aspects of the role - and most do it in a respectable yet firm manner.
The only 'downside' to this whole story is that the passenger was not offloaded (given the refusal) - lest he/she delay 100+ other passengers of an on time departure.
The passenger has no right to question the authority of the captain - and is greatly mistaken should he/she feel entitled to an explanation from the aircraft commander. The cabin attendant was no doubt acting upon his order - or policy that dictated that only appropriate persons be seated in such rows.
In every other aspect, flying aboard a sophisticated airliner may have become akin to travelling on a bus - but in no way does that give passengers the right (whether they realise it or not) to question the intent of those employed to keep the airliner safe. How much a passenger has paid has absolutely no influence on the crew's obligation to carry out their duty safely.
Unless you are rostered by the airline to operate the flight upon which you travel, you have absolutely no right to question the actions of the crew - whether you are a commercial pilot or not! Show some respect!
Before anyone argues with my sentiment - ask yourself - would your airline back you up if someone was hurt/killed because you put customer service ahead of safety?