Yeah, it's essentially cached eval, the key being where/how that eval is stored.
When you create a Flox environment, we evaluate the Nix expressions once and store the concrete result (ie exact store paths) in FloxHub. The k8s node just fetches that pre-rendered manifest and bind-mounts the packages with no evaluation step at pod startup.
It's like the difference between giving the node a recipe to interpret vs. giving it a shopping list of exact items. Faster, safer, and the node doesn't need to know how to cook (evaluate Nix). I don't know, there's a metaphor here somewhere, I'll find it.
Only so much room for magic, for sure, but tons of room for efficiency and optimization.