That's fairly easy to fix (in principle; I don't know what their backend is; it might require JS). But there's so little value in the navigation, that I'm not

That's fairly easy to fix (in principle; I don't know what their backend is; it might require JS). But there's so little value in the navigation, that I'm not surprised it works as an "MPA" (even though it feels janky). And that's all not done by JavaScript. The player, the animation, etc. still requires it. TBH, I don't see the point of this demonstration.