ED builds on the accomplishments of the original with the proc gen. It uses algo that generate stuff with a seed. Is used to compress data by avoiding to store billions of star system data. Instead you call algo and have generate the current place you're in with a fixed seed.And yet, it is true. If it was rng we would not be able to encounter the same things in the same spots every time. That is why the procedural generation in ED is fundamentally deterministic and not random.
In the case of the Stellar Forge it is even more true due to the fact that the star systems distribution and composition in it is not just based on an rng seed alone but based on actual galaxy disc matter density maps as currently known for the milky way. This in turn leads to very specific types of stars, systems composition, number of bodies, masses, temperatures and chemistry (and therefore colour) in them depending on where you are in the galaxy. If you actually watch the video I linked above you can learn about it, in particular min 13:05. It may very well have some random elements aswell but just to add flavour and fluff to the very deterministic core of the proc gen of the star systems based on actual galaxy data.
Not really, there is a very specific scientific base for how and where the systems are generated in the Elite galaxy, as per above. Not random or imaginary at all.
As shown above the stellar forge is not just a random algorithm. Not only it had to be designed to conform to known galaxy matter density distribution maps and produce logical results accordingly, but also it had to accomodate rationally all the actual existing celestial objetcs catalogued to date in it. The forge is so detailed that has managed to replicate reasonably well a certain number of recent real life discoveries like Trappist 1 or match certain theories like the ones related to the number of brown dwarves in the galaxy etc.
It is not a perfect system, but it is many orders of magnitude deeper and sophisticated than your "just a random based algorithm". Affording credit to it on the basis of scale alone (especially when you factor in all the actual real celestial catalogued items integrated to the system) is completely justified.
Proc gen often uses fixed assets to pair instead of total RNG, Warframes map tiles are crafted so they can fit together in multiple ways and generate different maps each times - but they all still play similarly.
Now why is important to have billions of star systems to visit I can't say - methinks a limited number would be better. If only for compressing content and make it findable for mortals.