A hybrid? It means he's the offspring of two entirely different species-- That is, he's only half-gem. Which was something I previously hadn't known was even possible before I met him. [You can practically hear her squinting uncertainly over this next part:] Didn't I tell you about this?

[Maybe she didn't. They must have just discussed Steven's numerous freaky godmode powers, not his body's weird genetic/gemetic makeup. Whoops.]