I think the problem is the conversation is the following:
The child appealed to their own expectations which probably can be reasonably linked to social tradition/expectations. While the child might be unaware of that, the woman certainly understands that.
The child commits a fallacy. That fallacy might not appeal to nature but fundamentally works the same. It is pointing to an “Is” statement to infer an “ought” statement.
The storyteller counters with an argument. That argument is also using an “is” statement to infer an “ought” statement. Whether or not, the intention is to show the flaw in the child’s reasoning; or to argue that hair is good there, can’t be known, as it is a casual retelling of a casual conversation.
The dino makes an another argument. That highlights the problem with using “is” to infer “ought”. Pointing at the flaw in the storyteller’s argument. The big problem, Dino failed to consider that she might was doing the same thing in a way that a child understands it. That she might doesn’t think it was a good argument at all but a tool to point the child at the issue. So the storyteller’s real argument might was the same as dino’s.
Consequently, I think you are right to say that the storyteller is required to said that her argument is trying to say hair should be there, to be at fault. But i think it would also be wrong to think dino tried to argue the hair shouldn’t be there, for the same reason. So basically people in the internet talking too casually to probably understand their positions and consequently you can’t have a meaningful conversation about it.
I think, as a body hair hater, a strong reaction to a random ass person’s body hair is ridiculous. And I guess, in this case, the concept of a random ass person’s body hair.