I agree that is unlikely that the student conduct charges are likely not related to Title IX offenses, otherwise I think they would have added that information to the legal letter (the "Trespass" letter) indicating if that was part of the review underway. Often they are taken in tandem (both Title IX charge and Student Conduct charge), but if there were issues related to Title IX it would have to be spelled out in the Trespass notice.If I may disagree just slightly, my guess is that BK was "trespassed" (WSU's verb) for the two altercations with his professor. I am speculating the professor felt his safety was threatened by BK's demeanor. All MOO, obviously.
If the issue were sexist grading, that was resolved by firing him from his TAship. If the issue were sexist remarks alone, I doubt the university would take the extreme step of banning BK from campus.
But I will admit again I have been retired from academia for over 15 years. It's possible there has been a sea change in policies since I was closely involved.
Also, I doubt that it would be related to "unfair grading", since the final grade for the course and/or papers/tests/exams along the way are determined by the course professor, not the TA. So if students weren't happy with the grades they received for the course, they would have an academic appeal process, it wouldn't be handled by the Student Conduct process.
I, like you, think it could have been related to the interaction with faculty in his department, specifically related to the various stages of discipline that BK failed to meet during his disciplinary process that we all read about. The things he was supposed to be working on were not achieved, and no progress apparently was made.