I wouldn't go suggesting some rare soil amendment. Evidently it works but so does compost.

Sand is not rare.
It is hardly anything like Compost
Compost holds moisture and keeps the soil cool
Sand does not hold moisture and allows the soil to warm more readily.

Volcanic Black Sand is uncommon.

So, if something is uncommon, you can't put it on your garden? It is anything but uncommon around here.

Boizeau, you have sinned, and now you must do penance. Repeat after me:

"I will not use the S word on GW."
"I will only garden in clay soil."
"Sand is from the devil."
"Sand has turned my soil into adobe."
"I must remove every grain of sand from my garden."
"I must drink the clay-flavored Kool-aid."

There now. Don't you feel all renewed?

In the picture we see sand on top of the ground, making it a mulch rather than an amendment. If it is also in the ground, then it is either existing soil or has been dug in.

In the latter case it would in fact be an amendment.

Stands to reason that heat-loving plants would respond to the warming of the soil due to the blackness of the sand.

I've actually mixed a lot of course builders sand into my clay flower beds along with truckloads of compost. No adobe here.

Adobe is made from straw/plant material and alkaline clay soil (caliche) not sand.

There is no sand in much of the desert Southwest despite how some view the desert. The areas in the Mohave and in Colorado and New Mexico with sand are rare. The Sonoran Desert of Arizona and Mexico has no sand but adobe is everywhere.

Well, in the case of that photo, the sand is over 3 foot deep, cause I root cuttings in that spot. In general I've been adding sand for over 10 years and in most places it is at least a foot deep. Yes, I have incorporated it into the parent soil.
Our weather is pretty cool most of the year, and what little heat we do get, is often wasted as the soggy soils use up the heat to evaporate this moisture.
The trick is to get the soil sandy, but not too sandy.
As we know, gravel pits are not conducive to plants--- even heat loving ones.
And thanks for the admonition about the nefarious nature of sand. I have been properly humbled down.

If there is a down side to this sand, it is that a lot of unusual trees try to germinate in it. I get a lot of seedling volunteers popping up here and there. It is apparently a great media for seedling germination.

Depends on what they are. Different plants like different soils. You can actually assess the conditions of a site using what have been called indicator plants.

That is partly why so many plantings have problems. If the plants chosen aren't adapted to the site and the site is not changed to suit them, the plants lose.

Plants do not adapt to different site conditions.