A rather minor issue uncovered in another thread: Legends Viewer 1.19.03 lists Blizzard Men as Animal People, while it was pointed out that they are slow learners, and thus ought to join trolls and ogres in the "animals" category.
I don't have the information what really counts as animal people. Categorizing a race as animal people only depends on the string ending with "... Men" at the moment. Without additionally parsing the raws or hardcoding every DF race, there is no chance of making this decision.
Thanks for explaining the reason.
I think the tag that they can become heroes is required for animal people to join civs (and I assume that rules out the subterranean animal people, although I haven't checked). I believe there are two hero tags, one for joining civs and one for allowing them to be played in adventure mode. Slow learner should disable animal peopleness (and it shouldn't appear together with the hero tag(s) anyway). EXOTIC_PET should disable them as animal people (that would cause them to behave like gremlins, I think).
Going by the "men" suffix would exclude Gorlaks (and include non sapients like magma men, but those probably never show up in settlements), by the way. However, I guess this kind of logic requires RAW parsing (which is far superior to hard coding, but I guess it's not something you like to do when there's no other reason to read them).
The above is from my memory of how it works approximately. I believe others actually know how it works.
Regardless, it's not exactly a major issue.