You can not supply 3.3V to a 3.3V regulator. There has to be some voltage differential. The result of doing that, would be a reduced output voltage, like say 2.5-3.0V. The only way to power the module from 3.3V is via the 3.3V pin that is provided. But if you only do that, it's not enough because it won't allow the level shifter MOSFETs to do their job. That is why I told you to strap the 3.3V and 5V pin on the module. If you just left 5V disconnected, the resistors would be in a strange configuration that might not play well with I2C..
It doesn't happen often, but in this case Adafruit documentation is absolutely incorrect (or, to be more generous - incomplete).