I made something similar. I wanted the keyhole look, but I made mine out of pallets. That's just what I had available for free.
Anything where the soil is higher than ground level would be considered a raised bed. Raised beds help with water drainage, not retention. So I'm a bit confused on how it can be "water saving". Is there another piece? Could you post a link to the instructions?

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There are several of these here in Clifton. The first one was built at the hardware store. That one was built of stone and mortar. They just added three at the retirement community where my mother lives. Those are built of stacked stones. They even had some for sale at the hardware store made of fiberglass panels. I thought they were pricey so I passed on those, but I plan to try a stacked stone one this spring. The moisture saving partially comes from the compost system that is a wire tube in the middle of the garden. They also line the edges with cardboard before you put in the soil. You can also use shade cloth or freeze cloth to extend the season of the garden. They did a tour last spring. I don't know if they plan another this spring, but I wouldn't be surprised.

Here is a link that might be useful: keyhole gardens

There is an American Indian ( hopi and Nem Mexican ) one that I saw on the web a while back that was done differently but was also an extremely water conserving. I went looking for it the other day and all I could find were instructions for the African ones. They are interesting.

Here is a link that might be useful: Keyhole Gardens

This is a different variation on the theme, a sunken garden. the American Indians, (Hopi maybe) have a wall to protect plants from the dry desiccating wind and use the pit to retain moisture and improve the soil in the bottom of the pit. It is the reverse of the african keyhole. They also found grids of these in ruins with canal system between them. Many early settlers copied the indian style of gardening because it worked in the environment. I don't think it would work on my land here in Central texas since the soil is so shallow and rocky. they aCTUally have deep topsoil here, just no water.. This is not the article I originally read a couple of years ago. I can't find that one.

Scroll 16 pictures down on the site.

Here is a link that might be useful: American Indian keyhole Garden

Sorry to be so late in thanking you all for your replies and info. Now I have a winter project that I'm excited about.

An African keyhole garden is actually a raised circular raised bed with a walkway leading to the center, where there is a cylinder of wire mesh or some such. Compostable materials are put into the central cylinder, where they break down and the nutrients make their way to the plant roots ... or perhaps the plant roots seek out the fertile soil near the center. I'm certain you can find a video on YouTube. A very clever way to make use of limited resources.