Without a doubt i'm blaming the manager but i'm not convinced it was racially motivated. If you are running one of those places, you don't make a stink about someone occupying a table unless you are having a shortage of tables.
I didn't see anything that gave the details of how long the guys were there prior to being asked to leave. In the videos they did not act like they were bothering anyone and like you said, they were calm and respectful from what we've seen. The facebook live video claims that they were making rude comments to the staff about them only making 40k a year so if that's true, they could have been calm assholes to the staff... I'd like to know more about what happened to lead the manager to actually call the police from both sides of the incident.
Either way, if you are asked to leave, just leave. Not worth getting arrested over something like that. The policy is dumb but they have it there so paying customers get access to their tables and restrooms. That's just a general statement though, not implying they should have been asked to leave in the first lace.