No why you say they were correct in doing so?
Well, I assume he was in the schools dorm. Schools have zero tolerance with drugs on campus--I believe all college kids sign a form before entering college that they will abide by certain codes of conduct. If another student said, "Student X is doing drugs in their room," then they would be correct in doing a student welfare check, as this would be violating a code of conduct (the student had drugs and drug paraphernalia in his room). I don't know what led them to the students room, but I assume they had probable cause to do a student welfare check. Further, we do not know the rules surrounding a student welfare check. The school may be allowed to conduct student welfare checks at their own discretionary. If this is the case, and the student signed off on it, then the school is allowed to conduct these checks as they deem necessary.
This is obviously depending on the schools rules. This is pure conjecture on my part.