Two <Anon> fc's?

While shouting a week ago, someone got a hold of me. Apparently the other <Anon> is from ffxi and they probably do not want to change their tag.
My question is, who has to change? I'm not a fan of changing Anonymous' tag from Anon to something but willing if the other group Master and I talk it out. Also, I hope they'd be willing to concede if it were to lead to that. I don't know how to get a hold of them or have even seen them.
Why can this happen? Has anyone else encountered a similar problem?