What happens if I plug a 2016 MacBook Pro into itself?
The new MacBook Pros have circuitry in all USB-C ports so that the charger can be plugged into any port.
Plugging a two-way USB-C cable will just make the device think that it's charging as technically there is a power source coming from one of the ports into the other.
It doesn't actually charge anything but the reporting is what's making the battery icon show 'charging'.