I don't know exactly what happened or didn't happen in this case, but in general, an acceptance letter is not binding if it is withdrawn before it is accepted. If any of the people who were given the letter actually accepted the offer of admission, then legally, they would likely have a strong case. However, if the college merely stated that the applicants were accepted (which I believe to be the case), it is not a contract until the offer is accepted, and thus it is unenforceable.
So, in this case, there is no issue of the students "accepting the offer of admission", because they have all "accepted" such offer in advance.
You can't accept an offer that will be made in the future. Early decision agreements are like non-compete agreements: the students promise not to apply to other schools early decision, and they promise not to accept offers from other colleges. You can be accepted early decision and choose not to go, because you haven't accepted the offer.