It's the whole enchilada, and there's more to it than pixel differentiation.
Agree. t's always been about picture quality for me. If a 65" 4k TV looks better than a 65" 2k TV past 7', it's because it's a better engineered TV, not because it has more pixels. What I take from that Sony paper is if all else is equal (dynamic range, black levels, etc), a 65" 4k display will look smoother and/or more detailed than a 2k display closer than 7', content permitting.
BTW, using that same Sony distance metric (2.3 x screen height), a 100" screen is 49" tall, so you need to sit 9.3' or closer to appreciate the resolution bump.