Doesn't make sense for his vocation to be something that he hates.
I think the way the crystal works, is to read your
current disposition. Reads your mind, mental state, emotional state, mana, analyzes your body, etc. Which is how it figures out what best suits the person.
MC has been the whipped errand boy for a long time, so that could have ingrained itself into him, similar to trauma. I mean, the crystal even knew Ruby by name, but did she ever touch it herself? Don't people need to touch it first, even just once, for it to work? If so, the only place the crystal could've gotten that information and made its judgement, is from Lloyd's own mind.