This can happen - you can be mixed up with another artist. I was mistaken for a notorious "serial scammer" artist one time because my username was vaguely similar to one of the several they'd used. Not super close but enough for this one guy to see it and go "hey wait a minute..." (my art style wasn't even remotely close to theirs - but he still sent me an angry note and email!).

It sounds like this person may be crazy, but there is always the chance that they are very mixed up?