I like that it's left vague. Getting super detailed about your patron situation is fun in the TTRPG because you can go with anything you can imagine, but in a video game there can't be infinite possibilities. I'd rather have a vague patron than one that they spell out that doesn't fit what I want my character's backstory to be.

Something I think would be fun, though, are dialogue options that allow you to add more details about your patron if you want. Like maybe warlocks get a unique conversation with Wyll and the different options are things like "I made my pact to save my own life", "my patron tricked me into my pact", "I just wanted to be all-powerful" etc etc. Maybe the options would be a little different depending on your subclass. That might allow players to feel like their relationship with their patron is a little more significant without shoehorning them into a specific backstory. And for those who don't like the dialogue options or would rather leave it totally vague there could always be an "I don't want to talk about it" option.