War of 1812 was fought because the British were kidnapping our sailers and forcing them to work on british ships, and because they were saulty about losing the revolutionary war.
I don't really give a shit if this guy sits or stands, but I do think that if he hadn't been born American he wouldn't be making millions a year playing football, and I also think the racial injustice he's protesting is the least severe its been since our founding, social media has everyone noticing things they never did before.
In short I think the reason he's sitting is mainly the exact reason you think everyone else is mad at him for sitting. he doesn't know any history.
RE: Star-Spangled Bullpoop