what do you mean years before I was born? Manga was barely even invented back then, and no, drawing human ears and animal ears at the same time is not normal even with manga, and is a fairly new phenomenon. Because artists with even a shred of self-respect and minimal drawing education, knows how to draw simple anatomy and would never mess up such a rookie mistake. It's the new artists that keep doing this, and it's lazy. As I said, No self-respecting artists would do that. Get Real. ┑( ̄Д  ̄)┍
Please do some research before making these kinds of statements. Manga was far from "Barely invented" when you were born, works like Astro Boy were already being published in 1952.
As for beastkin having human ears, a simple search will find art forum discussions from over a decade ago debating whether kemonomimi (The Japanese term for animal-eared characters) should have two or four ears. This isn't a new concept. There are also published manga from before 2000s, such as Hyper Police(1993), that depict characters with both human and animal ears.
Whether a character has two or four ears is purely an artistic preference, not an indicator of an artist's skill or the level of effort they have put into their work. Neither choice is inherently wrong, and many artists intentionally leave it ambiguous by styling the character's hair to cover the sides of the head.
As for AI, I agree that generative AI can and does produce anatomical inconsistencies. However, four eared beastkin existed for decades before generative AI became mainstream. Their presence alone cannot serve as evidence of AI usage. If ear placement is intentional and consistent across multiple panels or illustrations, then it is simply a stylistic design choice, not a reliable indicator of AI-generated art.

Already a few pages in, you see clear signs of AI Generation. I don't mind that, but when they make mistakes like this, it's super cringe. The Beastkin, or whatever they call them in this work, have 2 sets of ears. Human ears and beast ears, which is absolutely ridiculous and a frequent mistake that Ai Generated work commits. ( ̄へ ̄)