Think the change name thingy wasn't a real thing back then, it is quite a few years ago. I transfered to that server in 2008, and someone had my mains nick then. A low level char that was inactive for years, I couldn't change. 10 years later I could finally change back. So really doubt that was the case. Think they updated how that worked only a year or two back. Was in start of Legion I think.
Anyhow, if it was, I still can't use a name on my server then use it on the connected realm.