Without looking at the topic it is about: if you can copy the answer the question is (more than likely) a duplicate and should be flagged as such.
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Was this moderator wrong to warn me for doing this, or was I in the wrong for re-using parts of my answers?
My opinion? no and yes.
Comments were disabled on my deleted answer so I had no right of reply to the moderator, which seemed a little unfair, especially since his telling me off seemed a bit rude
In general I consider it not a good idea to use comments, questions and even meta for discussions about a moderation (mods probably will state to use meta). I would have done this in AU Chat to ask about this.
fossfreedom is not that bad a moderator and I am sure you are reading his comment in a way that seems to tick you off but that was not intended as such.