It's probably because a lot of paints don't have barring, but I do have to mention that barring can reduce the amount of black on a white. Not impossible though. I've seen "blue paints"- the spots being blue instead of black and sort of have one- there was a chick with a single blue barred feather in the mix.
I will say it is very unusual to have so much black on the tail if it really is a paint. Maybe it's not paint after all, but that black patch on chest screams paint to me.. hm. Hope there are more pictures of that chick.
I'm rather liking the paint too.. if there is room to do so, might try to breed for larger patches on my birds. Or at least give a slight preference for birds showing the patches over solids.. this was originally a project for larger/heavier birds.
Bought cornish x chicks at feed store last fall.. they did not seem to grow so huge or fast, maybe they were one of those slow growing broiler strains but they were on feed restriction while growing up. Most of the chicks were from a "cx" cockerel over my NN hens.