The hero stands before the 3D arrives.
A wireframe plane in perspective is drawn first, so the hero is complete at first paint. The WebGL core is a scene written for the theme, and it is only requested once the browser is idle, on a screen at least 900px wide, without Save-Data or a 2G connection, and never under reduced motion. It caps its pixel ratio and stops rendering when the hero leaves the screen or the tab hides.