I'm black and have the same observation, I currently live in Portland and everyone here seems to use Venmo, but when I was home during the fourth of July weekend back in Brooklyn everyone used Cash.
On the one hand I'm not entirely sure why you're getting downvoted. On the other hand I'm not entirely sure what point you're trying to make. If it's just casual racial stereotyping then I guess that accounts for the downvotes. But I thought you may have a broader point about the meaning of trust in ethnic/racial communities in there somewhere, it's unclear.
Why is it racial stereotyping that different communities would use different apps? As an external observer, it sometimes seems to me that one can't mention race in the US without inviting the allusion of racism.
It was meant to seed the latter discussion you mention. I am not privy to square or venmo marketing practices, but clearly that or some oddity about specific terms each app has results in such a measurable divide.
EDIT: for example this divide doesn't exist afaik for uber/lyft