Earlier quoted context omitted.
I should have been clearer - that was rhetorical to point out that if you and I use the same prompt and pick the same resultant image, it's harder to claim either of us have copyright. This is a gray area. The tools themselves could introduce some stochastic aspect so that outputs are never identical, also. None of this leads to an obviously clear cut legal position wrt copyright.
Your (and the other person's) set pf inputs drive a mathematical function that derives the same output. If we were all honest, we'd give up the idea of copyright altogether where ML is concerned. You can't get much closer to "It's just math, man" than what it is currently.
Of course, "it's just math, man" isn't precisely a legal argument, either.