In other words, “right but I want to quibble”.
“Right” about what? It’s true that Micha was using the term “naturalistic fallacy” in a sense other than the sense in which Moore used it. (Specifically, he used it to refer to arguments that infer something about the moral status of something from its naturalness.) But I don’t have any basic problem with that kind of loose usage as long as it doesn’t interfere with accurately understanding what Moore meant by the term when he used it. The “quibble,” such as it is, is aimed to clarify how Moore himself used the term. Which is not an issue that Micha raised, or one that’s particularly important to assessing his argument; it’s an issue that you raised in the course of a reply to him.
It’s certainly true that the issue of what Moore coined the term “naturalistic fallacy” to mean is tangential to this conversation. But misrepresentations of his view, especially those that are very common and very misleading, are worth correcting anyway, in the interest of accuracy.
I read him right without the benefit of seeing his later explanation
Well, no; what he said is that by “natural” he means those things which arise from a “spontaneous order.” But that explanation is itself ambiguous, depending on whether he means strictly a “voluntary order” (which may very well be designed), or instead an “undesigned order” (which may very well be involuntary), or both. Libertarian writers have often used the term “spontaneous order” to refer to either, or both, or have simply equivocated between the two different meanings from one use to the next.
If he means the former, you read him right; but then the claim is unresponsive to what it was supposed to respond to. And, since that interpretation is unresponsive, it made sense for Micha to suggest, out of motives of charity, a more responsive reading.
If he means the latter, you read him wrongly, and the claim is somewhat more responsive to Francois; but then it is underargued and almost surely false.
For what it’s worth, I don’t think that your reading of him is “off the wall;” I’m not even claiming that it’s wrong. My point is that whether you read his claim rightly or read it wrongly, the claim doesn’t get Arthur very far either way vis-a-vis his interlocutors.