Oh-that guy. I think I'll Google it instead and find something a bit more concise.

I'm always skeptical of anyone wearing a jacket (presumably because it's cold) while at the same time wearing sandals.

I am subscribed to MIgardeners channel and he can be informative.

And only a fool gardens in sandals - the chance of injury is high.

It's basically a variant of hugelkultur or the African "keyhole" garden.

I garden in sandals all the time. There are people that do it barefoot.

This is a variation on organic gardening that involves a lot more work. If one ads adequate amounts of organic material to the soil the same thing will happen and if that organic material is added as a mulch much less work is involved.

kimmq is kimmsr

A couple other videos:

Have the proponents of this done any controlled studies of how much (if any) water is stored, and what the effects are on the plants?

I have not seen a video that uses this method and a control bed. My guess is kimmq is correct about the organic matter. I would argue that using the rotting straw as a mulch instead as a reservoir would not only help retain the moisture in the raised beds but would double as weed prevention.