Conveniently, that's actually the case. A USB-C port should provide no power if there's nothing plugged in, and that's sensed by the data connection pairs. However, to support A-C adapters, you can fake it through the normal connection there.

This is why some things that have a C port won't charge on a C-C cable, but will on a A-C cable, because they don't actually talk to say they need power, but the A port will provide some power regardless, but a C port won't.