The regulator is bypassed when supplying 3.3 volts externally. If powering with 3.3V, you wouldn't be supplying 3.3V to the regulator. On the schematic, VIN is +5 volts while VDD is +3.3 volts. If +5 volts isn't supplied, the 3.3V regulator is off. So, when supplying 3.3V to the module via the correct pin, you bypass the regulator.