what the fuck is a "beginner" guitar in comparison

I think it has to do with price. Like a good beginner guitar is a cheap guitar that isn't flashy and won't hurt your wallet if you decide you don't want to continue playing

Spending over 500 dollars on a guitar you might give up on playing is not good for a beginner.

I'd assume a good beginner guitar is one that is playable and basic enough to work in a variety of contexts as the player begins to define his or her playing style and interests. Not entirely high end, but holds resale value reasonably well in case the player trades it in towards something better, and basic enough to be modified. As the player gets better, they they'll need more specialized features, with respect to such things as pickups or neck radius, so they would then either get a more "advanced" guitar or make the necessary modifications to the "intermediate" guitar to suit their needs as an "advanced" player.