That yao guai wasn't there to maul me in the previous quicksave. Neither was that giant radscorpion. I hate them! When I get the animal friend perk, it will not apply to giant radscorpions. Out of ammo for other guns, how did I fare against a GRscorpion with a sawed-off shotgun - Miserably, they laugh at pellets. I think that in the vanilla game, some script is following the player around and sometimes spawning things at medium distance away from the player.

If this is true, then forget about a dead is dead playthrough after L8. FNV didn't do this, I was always confident of what was ahead until the hit squads began to spawn. Am I imagining things? Also in Skyrim, I have seen things spawn right at my location.

No you're not imaging things but no there isn't any script involved. There are levelled creature spawn locations spread out all over the Wasteland which will create various creatures, depending on the player's level, every 3 game days. All you have to to is get within 2 or 3 cells away from them in order to have some random creature spawn there. Personally I kind of miss that sort of thing in New Vegas, not having them made it's version of the Wasteland kind of boring. While Bethesda could have done a better job of the random spawns, I prefer their approach to the set encounters that Obsidian used.

Actually there is a series of scripts involved. There are set locations random happenings can occur, including, but not limited to, some creature spawns. This differs from the normal creature spawning, however, so don't confuse the two.

The trigger bounds are based on trigger walls, not cell distance.

Yes of course you're right. But it sounds like (s)he's describing the regular creature spawns that occur around the Wasteland. The random spawns generally don't have Giant Scorpions, aside from that one encounter with the ants, and I don't recall them ever creating a Yao Guai except as a Scavenger's pet. And they only trigger once. It sounds like (s) c he's encountering creatures in areas where (s)he's already been.