If you watch the video, the place where he absolutely dominated the competition was his ability to drive a much better line through the corners, hit his marks, and carry a significantly greater corner exit speed. The greater the corner exit speed, the higher the speed on the straight. Low horsepower cars like the SRF, this is especially critical because every mph lost in cornering and braking takes quite a bit of real estate to make up. SRF's get 105hp out of their 1.9L SOHC Ford 4-cylinders... they are truly momentum cars. You bleed off too much speed, the guys behind you are going to eat you alive. He ran down the bulk of the field because of a little bit of sloppy driving on their parts, and a lot of him taking advantage of traffic and the leading cars fighting each other for position, which slows their laps since they're fighting each other instead of running perfect, clean laps.
At the start he fell back because he got caught in the "center lane" in the draft all by himself. All these cars, even production based cars like I raced, really benefit from the draft at 100+mph. It isn't just for NASCAR.

As far as weight goes, there is a minimum weight for each class, but that doesn't mean they all weigh the same. Cars are weighed at post-race impound, typically the top 3 in each class, to ensure they are not too lite. I always started the race about 80 lbs heavy (weighed with driver) to ensure that as fuel burned off during the course of the 35 or 40 minute race, I wouldn't wind up underweight.
Long and short of it is this guy was just flat getting it done.