Sounds like a lot of misunderstandings. It would make a good comedy of errors if it was actually funny.
Guy sees spare seat and asks for it
Couple try to keep a spare seat to provide space for the baby so they make up some fake excuse
Guy misinterprets the fake excuse as racism and gets self-righteous
Woman misinterprets self-righteousness for aggression and responds in kind
Guy misinterprets response for more racism and gets more self-righteous
Husband misinterprets self-righteousness for aggression against his wife and reponds with agression to ‘defend’ his wife
Guy sees aggressive response from an older, weaker man and assumes even more racism and ‘white privilege’. So he threatens the husband (seriously, wtf? Threatening someone with violence when they get off the plane should get you tossed off the flight!)
Captain has no time for any of this bullshit, so assumes the loudest guy is the one that needs to shut the hell up.
Guy thinks this is more racism, lets it stew and fester in his mind and blogs about it later.