Right at 8:20 is a mistake. The electrons are not "pulled" across the reverse-biased collector/base junction. The technical term for electrons being "pulled" by an electric field is "drift", but that's not what's happening.
It's the other mechanism for charge carrier movement that causes the current through the base/collector depletion region: diffusion. This is really just thermal diffusion- the injected electrons will diffuse into an empty space in the same way that air quickly diffuses into an evacuated container. Once electrons have diffused into the collector / base depletion region, drift due to the collector potential "pulls" them the rest of the way.
Anyway, BJTs are partially a thermal device, since their operation depends on diffusion!