No, there was a private group that required offensive material be posted to the main Harvard group to get access. The main group was private only inasmuch as you had to be an (incoming?) Harvard student.
This is no different than students posting offensive material on a physical message board on some main through fare on campus.
Edit: Actually, it's somewhat unclear to what degree and what material was required to be posted on the main chat, and what portion was in a separate private chat (still likely associated with Harvard in some way?). The article is unclear on these points. Harvard still has the right to gate admissions how they like (and they state that includes "moral character"), so if they are able to determine you are participating in actions they don't approve of, then they have grounds to reject you or revoke your prior acceptance. Just as if they Google'd you on your initial application and found verifiable and unsettling information.
This is no different than students posting offensive material on a physical message board on some main through fare on campus.
Edit: Actually, it's somewhat unclear to what degree and what material was required to be posted on the main chat, and what portion was in a separate private chat (still likely associated with Harvard in some way?). The article is unclear on these points. Harvard still has the right to gate admissions how they like (and they state that includes "moral character"), so if they are able to determine you are participating in actions they don't approve of, then they have grounds to reject you or revoke your prior acceptance. Just as if they Google'd you on your initial application and found verifiable and unsettling information.