"No tiling of structures"
What does that mean? Has anyone talked about this at all? What is the source?
My guess is - the easy way to do procedural terrain, is to have a set number of terrain features (a certain number of mountains, a certain number of hills, waterfalls, craters etc., down to even having sets of boulders/rocks) and you use the random number generator to position these to make it seem like natural terrain. It can look great at first, since each feature is hand-crafted, but after exploring for a bit you'd start to notice this mountain here is identical to one I saw on another planet.. Something like this would be the "tiled" approach, I'm guessing.
The harder was to do it is procedurally generate everything. Use the random number generator, and create rules to translate its output into terrain features which look as we expect. Each geological feature should be unique (or else very, very rare, depending on how the rules work), so there's no duplication of features. On the negative side, it does take a bit of work on the devs' side to cater for many possible outputs, they can't hand-cater for every single one which means you might find planets with floating boulders or impractically shaped mountains simply because they couldn't have anticipated that RNG output and their "terrain validation" didn't have any case to cater for it.