> This happens despite user's clearly communicated "prefers-reduced-motion" setting
Let's not forget the user's clearly communicated "prefers-color-scheme" setting.
Good point! Yet interestingly, that page seem to adopt to colour scheme preference just fine at this point. (Even dynamically.) It is fact that the gooey thingamajig keeps same weird colours in both schemes, but besides that, at least the main background and text try to reflect User's preference with regard to luminosity.