Crafted by a potter named M Sivasamy, this clay pot was designed to help keep produce cool for days.
He made a cylindrical pot made out of clay with a tap on one side and an outlet to pour water on the other side. A smaller pot fits inside the bigger one where you can place your vegetables which is then covered with a lid. The technology is simple — the water in the pot remains cool keeping the vegetables fresh and cool. - BetterIndia
For places with no or limited electricity, this could help immensely. Especially considering terracotta(earthenware) clay is almost used worldwide.
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"direct heat transfer" would require submitting the vegetables directly in the cold water since the air around the food is a terrible heat conductor. And the carefully cooled air gets replaced partially once you open the lid.
Good point. Indirect heat transfer; fixed.
Chilling the vegetables isn't about the cooled air, it's about the veggies in the clay pots cooled down directly by cool water.