but then why did his students not know about it?

if normally a professor or similar is put on leave there are procedures about informing students in affected courses, replacement professors being found or courses being cancelled etc.

the fact that this procedures seem to not have been followed is strange and looks like someone wanted this to go over without much attention

that his wife seems to be affected too is even more strange

that no even vague reason is told even now is also supper strange

I mean thing about it especially given how much it has blown up there is no reason for them to not at least give a vague reason, if they don't it's because they can't (e.g. court order) or they have a good reason to not want to (which is strange by itself).