Randomly generated almost certainly doesn't mean completely random.

It's much more likely that it simply means that each time you start the game, you get a different set of stars/planets.

For example, when you approach a star there's a 25% chance it will be main sequence.
If so, then you'll have 1d6+4 planets.
The first 1d6 planets will be rocky and the rest will be gas giants.
If more than 3 planets are gas giants then there's a 10% change of life in one of the rocky planets
and so on and so on.