Registered user logs in… to another user’s account (wtf?)

Can someone help me understand why this happens? I will gladly give any/all info upon request.

In short, I gave up on this project back in the spring and then last week I completely (or so I thought) wiped out the databases via the plugin WP Restore.

So, just now my friend/test user registered for the ‘new’ site I made, and when they go to their profile, it’s all the info that was entered from an old user from back before spring… um, wha?

Thanks. Pleaseeeeee help 🙂