I like to think that that Royal Guard book was just for him to make sure his D&D character was as acurate a knight or paladin as possible, and he kinda segwayed into the job through that.
As much as I would love to have canon tabletop RPG I keep wondering - in the world of MLP Moster Manual may not be RPG handbook. It may be your biology class textbook
@Background Pony
in b4 Flash Sentry shows up “I’m actually a human from a different world, but was told to come here to help you hook up with Cadance and make sure she get the crown.”