I think what is meant by comment in steemit is to reply to the post. Besides, comment is defined as "a verbal or written remark expressing an opinion or reaction". Therefore, the responder may post a remark (or response or comment) in any form that the responder deems fit, and it's the best way to express his/her opinion or reaction to a topic. As such, the remark or comment can be in any form such as a story, poem or written opinion.
Since steemit is a popular, highly engaging and widely used forum, it is expected that users can have different interpretation of a word, phrase or statement based on their unique background. Some things have more than one interpretation or meaning, and should not be rigidly construed as to constrain its literary expression, such as "a comment" can only be expressed or written in ONLY one specific form.
In fact, the suggestion of publication is a good one. Why let good writings go to waste. Authors of posts and comments have copyright in what they post/comment and should have the copyright reserved. Let's hope that readers in this forum respect the author/publisher's rights.
Thank you.