yuppers with no baffle its just spreading the pressure out over a large area lowering compression and not allowing the glow plug to hold as much heat as there is not enough hot exhaust being trapped in the combustion chamber.

When he pinched that tube he raised the pressure stopping the exhaust sooner allowing the glow plug to heat better, and the fuel to burn better. adjusting the length of the restricting tube will allow him to time the exhaust flow for the best heat vs flow ratio, which by the way is only useful at WOT

the reason a standard muffler works so reliably is the design guarantees enough pressure to always trap exhaust, a tuned pipe cant do that they can easily restrict to much slowing intake or allow to much exhaust flow causing a colder plug and lower compression with the setup he is using it wont work as well as a true tuned pipe, but since he is using this setup he may as well tune it the best he can