Comment by ajnin

The update in question here is #1809; so it's possible your brother encountered another data loss bug, which, considering their current state of QA, doesn't seem that unlikely.

By default the recycle bin has a limit of how much files it can store, and if you try to put more in there it will be deleted. It'll ask when you do the operation, but it if was done automatically as part of the update, who knows. A safety net with such big holes never made sense to me so that's why I always change the limit to 100% of the disk size. Your brother was lucky to recover his files.