Doesn’t Wyll specifically declare his patron as being a demon?
And yeah, not every origin character needs to be representative of a faction. Since there will be at least 8 characters, having them all represent a faction would get convoluted.
Wyll might not be aware that WoTC made a change there.
She's a half cambion. So she's not a demon but a half devil. And it seems half devils are still able to use pacts. Which is interesting.