Skatole can also build up in the meat of pigs, especially male adult ones, which is why some pork meat doesn't taste right. This is probably true for other meats as well. I've certainly encountered a similar off taste in lamb meat and duck meat before.
My theory is that in the synthesis of skatole, you end up with a lot of indole impurities that smell like feces even in small quantities. They can be hard to remove so people associate skatole with the smell. It's pretty common in chemistry, many chemicals have bad smells from minor impurities. Isopropyl alcohol is a good example, it has small quantities of acetone. Ethanol has small quantities of acetaldehyde. Really pure ethanol smells quite sweet.
But I don't discount your hypothesis. Upon further googling, it appears indole itself(with no groups on it) is also a known strong component in the odour of faeces.
As for boar taint(finally found the English term for it) it seems this is both associated with skatole and androstenone. So now I'm wondering what the actual evidence is that skatole is supposed to smell/taste bad on its own.
Can't find any sources on this happening in non-pigs though. So I'm starting to think the mutton and duck I had were just contaminated, probably by being raised in unsanitary conditions.
A good rule of thumb to avoid meat with boar taint I've found is to avoid cheap, smoked meat. Smoking is supposed to mask the off taste, but to me it just tastes bad and smoked.
So it's not so much that it smells like poop, just is as revolting in some more general sense. And DMT probably has a lot of bitterness to it(can't remember what it tastes like, honestly, but I remember its cousins AMT and DPT being intensely bitter, though I didn't vape them).
Weirdly, skatole also smells nice in very small quantities, and is apparently used in perfume.
So yeah, odour is a pretty strange sense...