They guy is rebooting the device and showing a non-public version Cydia icon appears on his iPhone 4s screen plus has a little chat with Siri by asking her what's the weather today.
And during the video, everything looks clearly working -- of course judging only 2:20 minute period of the video.
Here let's us watch a teaser video of A5 untethered jailbreak demoed in iPhone 4s.
Why he can do it? Simply because the guy owns Apple developer account and knows some technical skills to perform the not-finished A5 untethered jb for his iPhone 4s. Remember the process of the A5 untethered not finished yet, but unsigned code to run unapproved application with a secret key. Take this video as appeasement of your weary whether the iPhone 4s untethered is to made public or not, yes it will be made public. So don't lose hope yet!
Update: It is already released, dubbed Absinthe, download Absinthe untethered jailbreak tool for Mac, Windows, Linux. This is jailbreak iPad 2, iPhone 4s untethered with Absinthe tutorial.