I’m not sure what this tells us. Base clock is 1Ghz, turbo 3.7Ghz, but somewhere (hopefully between the two, but technically it could be less than 1Ghz) there’s a clock speed that the chip can run that produces less heat than the passive cooling solution can dissipate.
Presumably it depends a lot on the outside temperature and humidity. It's the reason I'm very wary of buying anything fanless since I live in a tropical part of the world.