Yes could be a donor but donor perks don´t have customize exit message, or yes? , staff member too?
That message had appeared when he/she left the game , no when he/she had been joining.
I suspect of his aim too , he change his name often and his profile is private.
For the momment you can close this thread , if i find anything for tell of , i will report him with that evidence , thanks and sorry for wasting your time.