People love to say incorrect things about transspecies, largely because it's a word that sparks an instinctive flinch response in a lot of people (because of the instinct to downplay species identity as not really as important/real as gender identity, mostly).
In fairness, the terms "physical nonhuman", holothere, endel, etc. are all pretty new, but the concept is not necessarily, though physical nonhumanity as a concept has has a pretty rough history with the otherkin and therian communities.
On the one hand, the belief in genetic causes for nonhumanity such as literal biological descent from faeries, elves, or other creatures has a long history in the community, and is actually far less accepted now than it was originally; and the philosophy of "this is my body, I am a wolf, therefore this is a wolf's body" has been at least moderately accepted for a very long time.
On the other hand, the community has a really bad history with self-proclaimed p-shifters consistently and repeatedly pulling young nonhumans, especially therians, into cults and abusive relationships by dangling the impossible carrot of teaching them to p-shift, which means a lot of us have an instinctive flinch response to anyone claiming to be "physically nonhuman" (and anyone outright using the word p-shifter is going to be shunned, and if I'm honest, probably should be, even if they're trying to """reclaim""" it - you can't "reclaim" a word that never referred to you in the first place, and if you do fit the actual meaning (ie, not "I acknowledge this is (at least to others) a delusion but it is my personal reality and I want/need to acknowledge that" kind of physical nonhuman, but genuine "I can teach you to p-shift, no listen it won't be a cult this time I promise, this time it's real, don't worry about the fact that I refuse to provide any proof of these claims" p-shifter), then... well, you are, bluntly, being dangerous to others for the exact same reasons the old p-shifters were).
Partially as a result of that, and partially as a result of a) ableism interplaying with b) the fact that "you're delusional" was a really common antikin insult back in the day (and still is tbh), the community (myself included) got into a really bad habit of firing back with "no we're not, because here's the definition of a delusion and we don't fit that definition" - without acknowledging the fact that that response was often wholesale throwing people who actually do experience delusions associated with nonhumanity under the bus. Clinical zoanthropes and other delusional nonhumans have been frankly not well-treated by the nonhuman communities for a very long time, and it's only in the last handful of years that that's really started to turn around.
.....soooo, yeah. This turned into a ramble, sorry ^^; tl;dr there's a long and complicated history with that, and there are reasons people get bitey on both sides of it, but no it's not as simple as "physical nonhumans are a new thing" or even "physical nonhumans have NEVER been accepted before".