Considerable speculation that some Movie feeds are being fed out on some platforms in 'Full' HD now. Not fully convinced myself currently. (My viewing is via the AppleTV Beta at the moment, so I can't confirm on a live commercial stream, I've disconnected my NOW and Roku devices at present)
If you can, enable the developer HUD on Apple TV. That will tell you what the Apple TV h.264/h.265 decoder is being fed in resolution, frame rate, bit rate, dynamic range terms etc. You do need a Mac with Xcode installed to do that ISTR - and possibly a free developer account.
It's very useful for seeing what the various OTT apps are being fed from upstream (Amazon Prime Video can often be half the bitrate of Netflix for UHD content...)