AFAICS it doesn't meet all aspects of the TV world's 4K spec, specifically the new colour regime. (99% of https://en.wikipedia.org/wiki/Adobe_RGB_color_space has to be a smaller colour space than https://en.wikipedia.org/wiki/Rec._2020 surely.)
> In coverage of the CIE 1931 color space the Rec. 2020 color space covers 75.8%, the digital cinema reference projector color space covers 53.6%, the Adobe RGB color space covers 52.1%, and the Rec. 709 color space covers 35.9%.
So yes, Adobe RGB covers less of the reference color space than Rec. 2020 (4k/UHD), but more than Rec. 709 (HDTV).