It was procedural at least in the sense that you couldn't store the data for all the planets in memory (or even store it on disk) on the 1980s systems it ran on. So you needed a way to generate the data on the fly.

yeah but you're dismissing the fact that this was just a pregen table of data back then. They made a map based on that, sure, but from that table came... everything else and you can't store all that data on floppy.

Similar techniques apply today. Pregen like 100,000 stars. Give them names and locations in the galaxy, treat them as your "locations of interest" with a seed. The rest can just be another cloud of particles with no interest and if the player visits, you can RNG whatever based on the seed. No two systems can share a seed. They can, however, share a branch.

Procedural generation can use a fixed seed, it's not too uncommon. For instance, Elder Scrolls 2: Daggerfall's map was procedurally generated, but is the same for every player.

They bragged about it being procedural in interviews.

What I was never clear on was the degree of cherry picking they did. There were 800 worlds on something like nine disks, each unique and peppered with minerals and artifacts.