Really feels like an exercise in making a bad solution fly (Generating a huge triangle mesh before rendering it). If you use distance functions(SDF) to your Julia set then with raymarching you can compute the surface directly without taking the detour via a huge mesh, dunno exactly what Julia set they are using here but other sets have been directly rendered for the last 10 year in realtime (adding pathtracing would probably set back the perf a tad but still be faster than this detour).

https://www.iquilezles.org/www/articles/juliasets3d/juliaset... (There are links to youtube recordings of the realtime renders as well as actual code samples on shadertoy)