That is just UI resolution
Try YouTube with stats for geeks enabled while watcing some 4k content.
It's 4K but the UI is rendered in HD. New version of Android TV will have 4K UI. IAlso other Smart TV OS like Tizen has 1080p 60 UI but the video is displayed at 4K. Your 4K TV always displays 4K even if your Android TV is set on 1080p resolution under settings.
Your 4K TV always displays 4K nothing more or less because that's the hardware capabilities pixels are fixed. Even on 1080p video it upscales it on 4K.
^ what these guys said. As well it adjusted and is showing the video you are watching at 720p. When you view 4k content, you should see 4k specs.
I noticed with kodi on mine, the UI renders at 1080p. With a 4k fire stick, kodi renders at 4k on the same screen
It's also worth noting, despite the correct answer above, that 2160p IS 4K.
I have a 1080p tv but kodi shows the screen resolution as 720p
Some apps limit ui to hd, no point going finer. Play a 4K video, and see what "Video Resolution" is. Check SmartYoutubeNext settings to see if video player is set to 4K - that app has a whole bunch of options iirc.
So does that mean that my Nvidia shield displays photos from Google photos in 1080p when screensaver kicks in?
I was surprised when I switched to new 4k TV from old 1080p that all the UI elements and photos look blurry, not as sharp as I would expect from 4k display.
I may be wrong here, but I'm pretty sure I remember seeing that Android TV typically renders menu and ui elements at 1080p but video and movies will take advantage of the full resolution of your screen.