That is essentially moot when it comes to whether or not punishment is valid. They clearly stated the reason for the punishment was not simply because they did it, but because they have evidence of them doing it even though they knew it wasn't supposed to be enchantable.
Now, if anyone that got a warning claims they had no knowledge of it being a bug and in no way discussed it, then I'd say the warning may not be warranted. But even then, Coraesine isn't exactly something that you just purchase willy nilly and throw 925 at just for kicks - It's a god tier material that makes logical sense that it shouldn't be enchantable.
Even when I saw someone ask on Discord whether or not it could be enchanted, even though I was not certain if it was or not, my initial thought was "Surely they wouldn't make a material that powerful enchantable!"
In fact, like the guy who asked on Discord, they too should have thought to ask. But even so, in this case the warning is not because they didn't know, but because there is evidence that they DID know.
And whether or not the evidence came from Discord is pure speculation. But even if it was, it can easily be provable by a GM that the person in Discord is in fact that player in game.