Duh, it's a tool-assisted speedrun. It isn't like he cheated or anything, he still cleared the game in little over four hours.

To remind you: Just because you can't do it doesn't mean it isn't possible.

Edit: Here's what the guy who showed it to us on the FFWiki forum said, because I was confused as well:

its a tool assisted speedrun, he can put the game in slow motion when needed to write his name in half a second, he can also save the game whenever he want, and resume it a 100 times from that point if he wants to, without us being able to see it on the video.
So there, quite whining.