As far as I know -- and I've double-checked this just now -- Yum Brands does not own Wingstop (which doesn't capitalize the "s", even though we all do it automatically). They own "Wing Street", which is a sub-brand of Pizza Hut. Wingstop is an independent publicly-traded company.
Wingstop created Thighstop as a "digital brand" -- essentially, a ghost kitchen run out of existing Wingstop locations. This is a trick that a lot of chain restaurants started doing since the pandemic. Denny's runs "The Meltdown" as a sandwich shop; Chili's runs "Wings & Things"; you can find others. You can only order from "Thighstop" online, but you can add a thigh to combos when you order from Wingstop if you're so inclined.
(And I have not lived in Buffalo, New York, but I have lived in the South -- and California -- and can assure you there are many "mom and pop" wing shops and local chains that…aren't great.)