• Since this is an action by moderator, I suggest you ask here or flag your comment. – user99914 Aug 21 '16 at 18:50
• Not providing a link to the Question or Comment/Answer at issue makes it something of a puzzle to find. Sometimes (but not recently) when I see a post that seems either not intended as an Answer but as a Comment, or fails as an Answer and would work better as a Comment having some beneficial content, I will flag it for Moderator special attention and recommend that it be transferred to a Comment on the Question. – hardmath Aug 21 '16 at 22:27

The answer was not transformed automatically, instead it was done manually by a moderator. A moderator can do this for any answer (if it is longer than a comment it would get cut off).

• Was it that bad? – user290300 Aug 21 '16 at 18:48
• I did not look into the content so far. I took your question as a technical one on the site mechanics. – quid Aug 21 '16 at 18:49
• On the content in specific case: First, that it was transformed to a cmnt also sends the message that you did contribute something useful (otherwise it would have been just deleted, not preserved as a comment). So the feedback is not as negative as you might think it is. Would it also work as an answer? Likely, yes. But also note that such decisions might be taken based on the answer in isolation and the style of your answer is comment-like. Would you have written instead, say: "Define your candidate for a norm functions as $d(x,0)$. Verify it is a norm." it's more clear it's an answer. – quid Aug 21 '16 at 19:04
• To make more clear the importance of style, let me give a still more risky example regarding style: sometimes a user answers in the style of a rhetorical question. This can be fine in principle, but when you review that in isolation and there you have the button: "This is a question posted as an answer." it is so easy to get tripped up. Because you are shown just the answer-post which is technically a question. – quid Aug 21 '16 at 19:12