whinmoor85 There’s a simpler explanation - an ‘under-extracted shot’.
You don’t need any particular dose size to do this and there is a stage of under-extraction before sourness & bitterness set in that can be syrupy & sweet with little in the way of off flavours. There’s no mystery or trick to it, just go shorter & coarser if necessary, until things taste good without being weak/bland.
It might be anywhere from 1:1 to 1:1.5 depending on how concentrated or pretty you want it. (In fact you can do it with brewed coffee at much longer ratios, so it’s more about grind than liquid out).
I can’t vouch for what they do/don’t do in milk.
A 22.5g dose is a double, even a triple in some people’s perception, the liquid out has no bearing on single, double, triple. They say in the video it is their standard dose.
A 1:3 shot is not 1 part coffee to 3 parts water, it’s about 0.2 parts coffee to 3 whole parts water. This is not a video anyone should be watching for any kind of education.
I don’t doubt it tastes good & if it tastes good, then do it. But the ‘whys & wherefores’ in this video serve more to confuse than enlighten. Standard fare for youtube coffee videos.