Edit: actually not sure if they are foreign nationals. Maybe someone knows if same applies?
The issue is of harassment and continued education at Purdue; not constitutional rights. It sounds like the pro China students were harassing Zhihao Kong. Purdue can decide what constitute harassment. 100% it's part of of every contract the student signs and agrees to as a part of their acceptance.
This is a false statement. The only regulation here is title VI and title IX. The administration of a public university is not legally part of the government.
Nope, you are wrong. There have literally been supreme court cases about free speech rights of students.
And yes, the supreme court has found that it is possible for a public school to break the 1st amendment rights of students.