I echo @
V10 's , and the fellow passengers, words. If they are GCH then they can book seats foc at time of booking. Their laziness in not doing so is nobody's fault except their own imho. They may have had a flight change for whatever reason but a call to the GL surely would've acquired the seats they preferred OR have let them know in advance at which point deal with it.
The fact that you were happy to move decks let alone seats if it was for another window seat ( I myself don't really like non window seats either) showed you were more than a reasonable person. Have to say I can imagine myself being the other gentlemen and even getting out of my seat to squat down( use of body language to show im not a threat) and quietly but firmly pointing out the above and that the preferred level of behaviour for GCH or anybody else with any form of status for that matter is to know the rules of the game better and not to disturb others.
Of course as with all walks of life being a GCH doesn't, I imagine, suddenly make you of better breeding but I bet we'd all love to know if they actually were or not.