because she probably copied it from somebody who doesn't know about titles non-existent empires.
His name is
Ludwig, Prinz von Bayern. "Prinz von Bayern" being his surename. He is said not to even use his name, but go by
Ludwig Bayern or
Ludwig Bayer. I guess he could also use his house-name "Wittelsbach", but if he likes to stay under the radar, Ludwig Bayern/Bayer makes sense.