In fairness the whole its not 8k non sense was a misnomer based on public's incorrect assumption that 8k is represented by Television standard of 16:9.
Although in reality (not vr ) doubling what has been sold as 4k (3840*2160) is not 4k it's less. Qhd we could say is accurrate as it has a min of 2500 to be called 2.5k.
Even 1080p is not really 2k its slightly less.
8k is nowhere close at 32:9 (7680*2160) or 16:9 (7680*4320) as neither is even close to 8000. In truth both are 7.6k.
With the excessive width the PiMax 8k would be accurately describe if you accept 7680 as 8k it would be 8k half height to keep consumers understanding specification.
But like you said manufacturers are not in the habit of educating consumers against their presumptions or how to understand how specs are applied.
While this doesn't cover 16:9 it will ilustrate well.
Take the 4k & extend it the full width & you have 32:9 or 8k half height.