I think it has to do with how they chase you after you pick a fight with 'em. I never was 100% clear on that one either, but that's what I've heard. Seems like some enemies will give up relatively easily (sight/sound?) but others will show up ten minutes after you "got away safely" (scent?). Again, I don't know if this is true ... so don't hold me to it. ;)
They do not drop fruit seeds. I have spent 100s of hours famring in the 3 craig zones and I slaughter almost everything there.
Seed wise:
Herb and Grain are the most common Vegetable more rare Fruit Seeds NOT dropped by tese. I believe the only saplings I've seen drop this so far have been caveberries. There is probably more but I would imagine that they are the touger ones.
I have noticed that when you get saplings to drop seeds, they tend to drop more of the same type of seeds afterwards. Does anybody know if the type of seed they drop is affected by the current day or maybe even moon phase?