1. When did this happen? The article makes it look like this just happened, but does not mention a date. I suspect the omission is on purpose (if so, boo!; if not, sorry, but please add event date).
2. The fact that the guy bumped off is rich is irrelevant (and going on and on about it dulls the message).
3. The fact that the seat the guy was downgraded was noisy (people arguing on both sides) is irrelevant.
IMO the main point is valid -- the person was first to the seat and in general whoever gets into the seat first keeps it in case of a seat collision or a duplicate ticket. He should not have been asked to free it to another passenger (who should have been downgraded instead and compensated somehow). But conflating this with unrelated issue to get on a "United stinks" meme is a cheap trick. My 2c.