It's quite correct. I don't know the intricacies of the system account management but a Standard FM Server installation runs under that user name.
You can however, at the beginning of the install presented with an option, provide a different user name under which the server will run.
YEs, there were discussions about that, but I don't remember when&where. There might be some tech articles - those, one never finds when needed...
THere are other potholes, i.e. never format the disk with the 'case sensitive' option. This one was added to a documentation after discussion on forums.filemaker.com
FMS on OSX has been using user "fmserver" and group "fmsadmin" for many years now... it's mentioned in every single article and discussion about setting permissions.
Your "FM Server" name results in the "fmserver" short name.