He could have generated a password in KeePass or similar, and then forget to save KeePass once he had the password generated, losing access to the wallet. I use KeePass and I know a couple of times I've almost shut off my machine without saving my new KeePass entries.
Indeed - now that you have given him an explanation I'm sure he'll use it (I was actually trying to see if he would come up with such an explanation himself).
Doh!
(maybe next time you might consider waiting before feeding people answers)
I actually wrote that before, although the forum said (While you where writing a reply, a member has commented. You may want to read that before posting a new reply)
So in future maybe you shouldn't be so ignorant!