Interesting guess, but that's unlikely to be the reason since I was just allowed to create a toon with a similar name, starting with those four letters.
I understand the inclination to be secretive about such filters and lists (to discourage people from circumventing them or to avoid implying that anything specific *not listed* is OK, among other reasons) but it would be helpful if we got just ever so more detailed feedback about why a chosen name is rejected. For example, whether it's considered vulgar, politically or religiously sensitive, references illicit activities, poses a potential IP/celebrity namesake issue etc.
Speaking of inexplicable name rejections, an example from my experience is "Mildred" (alone or in a combination with another name). An existing if somewhat archaic English given name, it is presently considered an "invalid name" by SWTOR, yet apparently was allowed at some point in the past, since at least one of the servers has a toon with that exact name. Is it a slang term I don't know - not being a native English speaker and all - or perhaps a trademark or fictional character IP issue, or something completely different?