I was trying to find out what my username is to log in and I got this rubbish response (no way is seanspotatobusiness a common word on this forum):

How odd!

Plus, I didn't think you could do a username search without being logged in already. Maybe it wasn't a username search, and the search tried to break up the string into words? Like maybe it searched "sea"....although that doesn't seem all that common.... Or maybe it recognized "an". Or something like that?

I have no idea how the search works here, but I've had trouble with getting that same exact error message in the past. And also in situations where it didn't make sense. I think it told me "pen" was too common once. I've never been very impressed with the search here, and not sure how much it can be configured by the admin. My best guess is that it would take some study, to learn how.

I know you're not supposed to, but I keep a notebook with all my login creds. Since I live alone, there's not much chance it could be used maliciously. Even if there was a break-in and they took the laptop, how would the thieves know there was such a notebook?

Edit
But can't you use your email address, to find out your username, or change password? I guess some sites need the username, and other sites use the email address. I don't know which one phpBB uses.

The error phrase "too common" is just the phpbb stupid way of saying there was an error.

You can repeat the search with any string longer than 14 characters and get the same result.

A better search might be "sean*" without quotes, using the star as a wildcard.