Your second link is literally Anthem passing provider fees (in violation of their contract, sure!) through to customers. The bills were from providers.

Fuck if I know what's going on between Medicare and UHC. It's a mess. Medicare Advantage is a hybrid Medicare/private system; once again, whatever fees were being passed to Medicare, they were coming from providers. Insurers can certainly inappropriately deny coverage, but they don't generally make de novo charges up. Charges come from providers.

Upcoding scandals, which literally appear to be what the UnitedHealth link you provided was about, were exactly what Anthem was trying to control for with its new announcement.

Medicare Advantage is a capitated program. The provider fees aren't being passed through to Medicare.