Thats how warlocks work in DnD too, casters that made pacts with something powerful, like demons or faes.

Funny enough, I have to watch some YT videos on it to understand the difference between Warlocks and Sorcerers. I guess warlocks actually do meant some sort of evil pact with an unknown deity that isn't God

Not necessarily evil. Just a pact with some powerful magical entity.

As for sorcerers, they are basically born magical. As in, one of the ancestors or parents was a dragon, or an abberration, or a celestial or demon or something. Something with magic fucked your grandma, so now you are born with magic and can manifest it at will, but not as varied and (often) not as powerful as a Wizard/Magus, who has to learn the spells, gather components, and memorize spells as a daily ritual before being able to cast em. Basically Impromptu magic thats weaker or less varied vs magic that needs more prep time but can be more varied and powerful.

As for god, well, only divine casters get their magics from deities. And not necessarily good deities. You can be a cleric or oracle or paladin of an evil deity (well, more like anti-paladin in the last case).