Looks like I was simply wrong with assumption that GaN could only emit blues and there are plenty of efforts made for green and red GaN LEDs with such methods as Eu doping as well as some InGaN and AlGaN structures. That makes it not pure GaN based, but there is no such things as undoped semiconductors anyway. I believe QDs are not usually made out of GaN and it also doesn't seem to be in line with the wordings used. Your theory of this being based on multiple LED sounds likely, yeah.

  https://compoundsemiconductor.net/article/114125/Realising_red_GaN-based_microLEDs_with_europium-doping
  https://pubs.aip.org/aip/jap/article/123/16/160901/400705/Perspective-Toward-efficient-GaN-based-red-light
  https://www.researchgate.net/figure/Color-online-a-Schematic-of-an-InGaN-based-red-LED-epitaxial-structure-b_fig1_355092457
  https://www.tytlabs.co.jp/en/english/review/rev402epdf/e402_007kato.pdf