i think the simplest thing to compare this too is a wrestler
"What is the Rock's real name?"
your first thought is ALWAYS going to be dwayne johnson. not a single person is going to think douglas johnson
thats what people mean when they say "real name". its not suggesting douglas isn't part of his name or anything like that, its that people naturally associate first and last name as "real name" (or all together, but never middle and last alone). some people don't have middle names too because its not culturally normal and so first and last name will always be the default "real name"
He doesn't even go by Douglas so this isn't even a valid comparison. ---