Yes, it's a matmul; many color models just boil down to simple math. For example, look at Li and Luo's 2024 "simple color appearance model"[1], which is very similar to OKLab (just matmul!), and created for many of the same reasons (just an approximation!). Like OKLab, it also improves upon CAM16-UCS hue linearity issues in blue. Ironically, Luo was one of the authors who proposed CAM16-UCS in 2017. And, although it certainly improves upon CAM16-UCS for many applications, I'm not yet convinced it is superior to OKLab (you can see my implementation here: [2]).
And I think you might be mis-remembering Ottosson's original blog post; he demonstrates a gradient between white and blue, not blue and yellow.
And I think you might be mis-remembering Ottosson's original blog post; he demonstrates a gradient between white and blue, not blue and yellow.
[1] https://opg.optica.org/oe/fulltext.cfm?uri=oe-32-3-3100
[2] https://github.com/texel-org/color/blob/main/test/spaces/sim...