Satoshi was the creator/admin of the forum. Back in the day, people can post in the forum as "anonymous". No sign up was required if I'm correct. Satoshi added the post as administrator. I don't think there's anything special. Moderator may check what has been edited as they most likely has the right to check the original version of the post.
I also had the vague idea that "guest" posting was a thing back then (I actually mentioned it and then edited it out of the OP, to keep it more focused). But I'm not sure if that was an old forum (SourceForge) thing or not, which would predate this post, I think?
Either way, I don't think it matters much, because I can find examples of posts that were both made and edited by "Anonymous" or made by "Anonymous" and then edited by "davidonpda" (like
this one). But this is the only example I could find (so far) of one edited by "satoshi", although I admit I haven't looked carefully.