> So, if that’s 2K, what’s the real, DCI 2K, then?

Exactly! It was so bizarre when they started doing it. Basically, it seems like they went from the "#K" being based on the vertical resolution (sort of) to it being (vaguely) based on the horizontal resolution - except continuing to use both inconsistently. And 4K became widely used to refer to 3840, so it doesn't even mean DCI 4K (which is actually 4096).