Recently, I found a user that had a reputation under 50, so he couldn't comment. Instead, he put the comment into an answer, which people shouldn't do. I flagged the answer. After I rechecked, one of the admins or moderators deleted the "answer" and put it into a comment which had the author as the person under 50 reputation. Did a moderator do that? Can moderators do it? Or was it some community admin?
Yes, moderators can change an answer into a comment and attach it to the question (or any other answer) within the same question thread. Usually we use this exactly in the situation you mention (low rep user asking a clarification question).