In the video, starting from 0:44, it is a clean saw, not in the same condition as the saw was demonstrated cutting.
To evaluate the two saws (Bosch vs Kapex 120) in terms of dust collection, both must be used under the same conditions (including cutting the same kind of wood, hooked to the same type of vac, etc.).
It is irrelevant whether the Bosch saw in the video was connected to a vac or not, because when I use my Kapex, it is always hooked up to a vac, and that is the condition I would like to see in any mitre saw video purported to show its dust collection ability. The Bosch's dual chutes design may or may not make it better than the Kapex 120 in the dust collection aspect.