He,s over exaggerating the term ,its more of a distrution of weight .Zero mast foot pressure results in tail walking and out of control too much weight back away from mastfoot,common with first planing experiences in footstraps and harness.

mast foot pressure is a way of controlling board trim, too much pushes nose down too little and you tail walk. It's not only about riders weight.

He seems confused.

Mast foot is your foot closest to the mast (front foot). what he's referring to is mast base pressure. They are two different things which will produce different results when described properly to a learner.

I think Cookie is questioning (probably prevalent) usage of the term in coaching circles when teaching beginners / intermediates / improvers. To the uninitiated - the concept of mast foot/ mast base pressure, can be easily misunderstood - and may lead to perverse outcomes, such as the ridiculous 'hanging off the boom' bit he demonstrates during the video.
.
Mast pressure pretty much drives all all windsurfing maneuvers, but it is quite a subtle technique. Most of the time I'm not even aware I'm applying it. If I tried to focus only on applying 'mast pressure' when learning to beach start / plane / get in the harness / gybe, but didn't even know what doing it correctly it felt like, I'd probably start doing all sorts of weird stuff.
.
Importantly, if we learn to do maneuvers optimally from the outset, mast base pressure is just a natural consequence of good body position, balance and vision.

still DIY, but anatomically correct mastfoot protectors could relieve so much confusion