yes, it's "adaptive"...
by the way, it doesn't require a super-wide bandwidth to work at max rate, the problem is that it's not working the same way on all devices...
basically, if you want to be sure at 100% to reach always the top picture quality, you must have an apple tv 4K (last and forelast generation)...
in particular, it doesn't work well at all on the android tv/android box devices and on the amazon firesticks (even if on this last device the reports are controversial, some people can see the streams at 1080p/50fps, but many others can only go up to 720p/25fps -which is my case, despite I have a 1 GB FTTH broadband connection and my devices are all connected with cable, no wifi)...
moreover, some streams are actually uploaded at 25fps frame rate by discovery*, so, it's not up to your device/internet connection...it's their fault...
*here in Italy, they only kept 25fps streams for all the euroleague/eurocup games without Italian teams on the floor, for instance...
or for some more sports with minor interest in the average spectators (very exigent people like me don't count at all in Italy, as we're such a minority)...
our main tv/tech forum is full of people complaining against discovery, but it looks that they don't care at all...