I wish I could figure out what happened initially, but everything is paywalled. So my understand is as follows (and please let me know if I'm wrong):

The ruling seems to indicate that OfS (which I think isn't a Sussex office but a governmental body?) appointed a known anti-trans advocate to lead an investigation into whether Stock's speech was illegally stifled.

OfS decided "yes" and levied an unheard of fine.

Sussex appealed, and the high court (which I don't think is the highest UK court) basically ruled the following:

That OfS decided before the investigation started that Stock was right, made multiple errors in their investigation (claiming multiple things were official policy that weren't, etc), ignored the balancing factor of the effect of OfS's ruling and Stock's position student's rights that were required to be taken into account :

Basically that OfS was biased, was acting as Stock's personal attack dog, and made multiple errors of law and fact in the process of attempting to punish Sussex as a lesson to the other Universities that TERFs and other anti-trans bigots have more rights and are more important than those of students, and especially trans students whose place is to accept the hate and abuse that folks like Stock want to shower them with.