@noblegiraffe
If you’re isolating, you’re not supposed to leave your house. That applies to everyone?
If there is a positive case of coronavirus, then the household of that person, and their close contacts over the 2 days before they became symptomatic [and any close contacts once they were symptomatic] have to self-isolate. Self-isolation is stricter than lockdown - no member of the household should leave the house, so no walks, going to work, shopping etc.
That is the rule for everyone, wherever they may live. In a hall of residence, if there is 1 case in a single flat BUT that flat has been following proper social distancing guidelines - rule of 6, strict SD outside the household etc - then only close contacts within the flat [probably the whole flat] will have to isolate.
However, where you have multiple cases - up to hundreds of cases - in a hall of residence AND strict SD between households / flats and individual students hasn't been observed, then basically everyone becomes a close contact with a case, and the whole hall has to go into self isolation for 14 days.
It's not a student thing - well, the behaviour and lack of SD is a student thing, probably. It applies to any place or any group of people where this situation of multiple cases and a large network of close contacts arises.
It was also entirely predictable. Anyone going to university this year, should have known that this was an obvious risk, and also have realised that returning home was not going to be advisable or in mny cases possible. DS went off a couple of weeks ago, and unless his institution closes completely along with his accommodation, we all knew when he went that we might not see him until next Spring.