@MWolf, yes, I agree, my speculation is that this bizarre little incident probably was fueled by the prof’s oversize ego. Either he enjoys exerting control for nonsensical reasons, or prof thought he was being magnanimous by offering up the newly free seat (because it was closer to the student’s assigned seat), and grew irate when student didn’t take him up on it. I picture student responding with “Thanks, but I’m good,” while prof wanted him not only to move seats but to profusely thank prof, “Oh, thank you so much,” bow, scrape, bow, scrape. And do I think racial bias played into the prof blowing his stack to the point of calling the police (stereotypes of African Americans as ungrateful, sullen, difficult, etc.) – you bet I do.