To me this edit contains additional information that should be added in a comment, not an edit to the answer. As it stands, this edit makes it seem like wizzwizz4 added the content, not an outside user. We don't really want to be putting words into another user's mouth.
It probably shouldn't have been accepted on principle. However I (as the author) would have accepted that edit, although with a little modification, because as it turns out most of the information I used to create the answer originally came from the page (despite going through many a modification on other sites).
I think I have seen differing views on this across the different sites, and although I am not sure about this specific edit, I think there is a legitimate view that answers become communal property which should be edited to improve them.
So there is a question of etiquette in allowing the author of an answer the opportunity to react to a comment, but if that comment had been on an old answer and subsequently ignored, I don't see that editing the answer directly (without vandalism) falls outside of the normal operation of the site.