This sort of thing is older than generative AI. For the last couple of decades it has been impossible to share an interesting photograph without someone claiming that it was Photoshopped.
I can tell from some of the pixels, and from seeing quite a few 'shops in my time.
That's what people say - that they can tell if something has been 'shopped. And maybe they can with particularly clumsy manipulation. But the fact is just with as with people claiming something is AI, they often claim that something is Photoshopped which is later shown to be true.
That's been going on a lot longer than photoshop and digital photography.