My uneducated guess is that it is the mainstream Protestant vote breaking for Kamala in a way that won't be reflected among evangelicals. These are the old school church ladies and not the new school holly roller/prosperity gospel types. If that's true I expect to see this break the along the same geographical divide (i.e. more in the mid-west, less in the south). I have nothing but raw instinct to back this up. But that's my suspicion.
ETA: With all that being said, if true, that's still ridonkulous good news for Kamala and spells victory anyway, I think.