You couldn't have known. 

This was a fake question acting as a bait for spam answers. These spammers are getting more clever now. They post real questions and wait a few days before providing an answer with a different account. 

In that case we knew the user names and had several other indicators that the question was spam.

When you're reviewing questions about password or file recovery, be a little suspicious. It doesn't hurt to flag the question with a custom flag telling us what's up. There are a few telltale signs like linked network accounts with similar questions, or copy pasted question text.