You figure a joint is APPROX. 0.7 - 1.3 grams depending on how much you pack in. And also take into account that you're usually sharing a joint with at least 3-4 people. When I smoke it's usually a bong and I would estimate that I use APPROX. 0.3 - 0.4 in a bowl. So, yes smoking over a gram of weed in that short amount of time is a hell of a lot.
As someone else stated, it also depends on what potency of marijuana you are inhaling.
From what I saw in this short video, the conclusions are about what I'd expect. A normal amount in your system doesn't impair you all that much. Maybe a little more paranoid but for the most part, motor function doesn't seem to be all that bad. Once you get to the point where the girl was, it definitely would make a big difference. Such is the same with alcohol. Driving with a 0.06 BAC compared to a 0.24 BAC is an enormous difference.