In my younger days, I used to draft like that, too, buses and trucks, and have been easily towed around 50mph, so as has been pointed out, whether it's faked or not, it's certainly very possible to do that.

The other thing that has been pointed out and that is true is that it's a fairly risky undertaking. In my experience, I doubt the truck breaking would cause any problem so long as the cyclist is aware; certainly the bike can out-stop it given a reasonable response time. EDIT: I watched it again, and he's awfully close! He could fall back a little and still get the draft, though it would be little more turbulent and difficult to stay in, but he'd gain a little look time.

There are, however, other factors that can cause big problems, e.g. road hazards and the possibility of an accident.

It's a calculated risk, and the road in question looks smooth and in good repair, and traffic steady for quite awhile; no lights, no access.

It is fun, though!