Have you noticed that the size of the USB C plug is such that it is possible to insert it to an US outlet. The USB C connector just fits to the wider prong hole in the US connector (slightly too big for thinner prong hole).
It is even possible to make the USB connector to make contact with the metal parts inside the connector (depends somewhat on the USB C connector and outlet construction if it can make contact).
Fortunately the wider prong connects the neutral wires (wires carrying unused electricity back to the breaker panel), so it does not shock you badly if the outlet is correctly wired.
It is the narrow prong that connects the hot wires (wires carrying electricity from the panel to an outlet or a switch). And USB C cannot fit into this.