Have to use SerialUSB on M0 to print to Serial Monitor, but variant.h says otherwise

Here is the relevant part of `variant.h`:
https://github.com/arduino/ArduinoCore-samd/blob/bab730bf6e4716601fe51cbb692d9b25cea90386/variants/arduino_mzero/variant.h#L203

Am I doing something wrong?
