Can anyone explain me is the following sentence a joke or what?
Even as students, broke and staying in the worst accommodations he had ever experienced, with the temperamental heating and bathrooms they had had to share with dozens of others, thing has never been like this. They'd shared a single bed on box-bedroom so small that they had to walk outside for a change of mind, but they didn't mind, in fact they loved being so close to each other.
Maybe it's also a play on the expression 'a change of air'. I haven't checked any corpora, but certainly, in the UK at least, 'going outside for' collocates very strongly with 'a change of air. Whatever the reason, the writer plays with 'mind' as well.