The first part is oversimplified to the point of inaccuracy.
There's a longstanding tradition that white and non-white students separately voluntarily participate in various educational events focused on racism for a day. The events for non-whites had traditionally been off campus, while the events for whites had been on campus. Last year, they switched the locations. There was never an understanding that all whites or all non-whites would attend the events and thus that, for example, non-whites were not welcome on campus in past years or that whites were not welcome on campus this year. In fact, it was pointed out that the event locations would not even be able to accommodate that. Some level of participation was strongly encouraged, but the extent was not dictated (so, for example, last year, a white student might attend one of the off-campus events in the morning and then go to class in the afternoon).
And you'll have to clarify what you mean by "witch hunt" before anyone can tell if that's true or false. It appears that Weinstein objected to the location switch of the events (his colleagues say he misunderstood the nature of what was scheduled) and became the target of broader protests, and I think students clearly acted inappropriately at the protests and that Weinstein was unfairly targeted.