For what it's worth, as a materials engineer, I have encountered this kind of behavior professionally a couple of times, both from Japanese men. One guy when I was interning in Alabama ("You go to MIT? Is your daddy president of the university?"), and a student when I was TAing graduate thermodynamics (he never came to tutorials or talked to me about his poor grades, and I got the impression from him that my sex was the reason why not).
Maybe a predisposition to believe that Japanese men are sexist can cause one to believe a Japanese man ignored you as a TA because you were female, when there other plausible explanations, such as his not being serious about the class or his being reluctant to get help from anyone, male or female. You are generalizing based on a sample size of two.
