I have had that trick pulled on me several times in my flying career when I've been in a prime seat. I always tell tem to get stuffed. The other thing some of these seat bullies do is to make sure they get on first, grab your assigned seat and then suggest that to avoid "further confusion" would you mind taking their seat. I always tell them emphatically no and in one case had to bring on the GA to enforce getting my assigned seat as the jerk said he was now comfortable in my seat and had his bags in the o/h just above the seat and needed his stuff during the flt.
Some people are wacko.

I don't think it was per se race related but you being Asian on a LH flt might have made him think he was more important to LH as he was probably more likely to be a higher ranking FF'er than you are which still makes no difference.

However the purser was totally wrong in the way she handled the situation.She sould have first asked to see your BP to be sure you werein the right seat and then gone to the gate agent to sort it out if there was a duplicate seat assigment. It could be the guy was a friend of someone on staff for that flt, but so what.