They had their chance to deal with this during the disciplinary process, and it seems that between that and the appeal, their regulations and decisions were not sufficiently watertight to withstand legal challenge.
There is a huge gap between "would, in principle, fail to withstand challenge" and "has, in practice in this particular case, failed to withstand challenge". The university always had the option to say "fine, if you think we are in the wrong, bring a legal action". Warwick have deep pockets, and the self-immolation that would be involved in a privileged man showing that material in open court, and arguing it was OK in open court, would be sufficient to power Coventry.
One of the failings of universities is that they are reluctant to say "think we're in the wrong? See you in court". That leads to a very defensive, very fearful attitude towards problems like this. Yes, university statutes are usually inconsistent, particularly in pre-92s whose statutes have grown up over decades or centuries. Yes, university disciplinary processes are not always set up to deal with the full spectrum of issues. Yes, all too often there are attempts to mediate and resolve issues informally which then blow up in the university's face if it does become a formal process.
None of that stops the university from taking a decision to use the powers available to it and then saying "disagree? see you in court". Unless the initial decision were manifestly unreasonable ("Wednesday unreasonable" is I believe the legal term), the worst that is going to happen is that a court is going to impose a different outcome which is probably within the range the university considered in the first place. And the complainant would have to fight the action in open, reported, civil (balance of probabilities) court, which would in this case be extremely uncomfortable for them.