I edited the answer to this question with information which is a complement what the user already answered. I could have provided the additional information in a separate answer, but since the existing answer was already pretty good, I opted to add to it rather than trying to gain some rep out of a simple answer.
However, my edit was rejected, and the reject reason mentions "This edit was intended to address the author of the post and makes no sense as an edit. It should have been written as a comment or an answer". My edit was not a comment, and was useful information.
I did post a comment to the user who provided the answer, to let him know he could remove my edit if he felt it wasn't appropriate though.