Users gain the ability to modify other people's posts, including the ability to convert answers to comments, if they are promoted to the Expert status (or a higher ranking). We hand out those promotions sparingly, and only to users that we trust. Therefore, if your post was converted to a comment, you can be assured the decision was made by somebody who knows what they're doing.
I assume you are referring to this comment? It was my own decision to move this post to a comment. The reason I did that was the post's briefness, and how much of its content was not intended to answer the question, but instead to gain clarity on the question (which is a function of commenting anyway). Essentially, if the question you're answering requires explanation, your reponse should be longer than only one line.
For context, I am a mod; so your posts were not edited by someone who is not a mod.
