Im so sorry to hear about your team having to go through this, especially the artist, it's like these people forget that AI is trained off of real artists, and so many of the "flaws" are things that you find in real artists work, there is no way to be 100% certain just by looking.
Unless there is 100%, undeniable concrete evidence, they shouldn't even *mention* AI in connection to someone's work, unfortunately I feel like some of these people do it maliciously to cause doubt in people viewing the artwork, and stress in the artist 😔