Every itemtype has a "subfamily" that dictates, among many other things, whether the player can click on it to interact with it.
For example, you might have noticed dogs and cats in towns, but you cannot click on them. This is due to them having the subfamily "SUBFAM_LIFE_ANIMAL_ATMO".
Most corpses have "SUBFAM_INTERN_STATIC" which means they're basically just part of the environment.
Some, however, will have need to be interacted with for quest purposes. So they are given a different subfamily like "SUBFAM_LIFE_ORC". That corpse is one such example.
You might ask, "so what quest is it part of?" but the thing is it's not, at least not that particular one. Instead there's probably some other quest where you click on a dead Orc, and the devs just reused the itemtype as "decoration."