I don't think he edited anything. The forum shows a pen next to the post header if it is edited. (left to the time of posting.)
One can look at the post histories. This also includes changes to the title. I just tested it with one of my topics.
But there are some bugs it seems. (So i could be wrong) After changing the title and reverting changes, it does not show further edits.
Ok one can trick this edit thing. If you edit something make anther edit revert the last edit and it seems your post has never been edited. (And there seems to be a bug if you edit too much.)
I played around a bit more with it. The edit thing works again after one waits a bit. (So if you edit your stuff very often within a short amount of time it does not show the edits.)
If you ever break the edit history you can not look at how the original post looked like.