> I've heard a minority of (seemingly highly educated) people prefer to say "Castellano" instead of "Español"

I would expect castellano in Spain, and español in the Americas. Does this align with your experience?

Not always. People from the center and west side of Spain typically refer to it as "español" rather than "castellano". Nonetheless, it's true educated people typically refer to it as "castellano" as well as other Spaniards that live in a region where other official languages are spoken.

	▲	schoen 2 days ago \| parent [-]
		And some of the people I was thinking of who said "castellano" were from Latin America (though this is clearly a minority usage there; maybe some of those people even had Catalan-speaking friends or colleagues or something).