Just because using different WB settings to demosaic the raw data is non-destructive to the raw data doesn't mean one WB setting will be more or less noisy than another. It's not so much that you will get equal quality regardless of how you choose to interpret the raw data, but rather that regardless of whatever interpretation you choose to use for the raw data, that interpretation does not change the raw data contained in the file - it only changes the way an image created from that data looks.

Beyond that, a raw file has no white balance. The raw data is a set of monochrome luminance values. When the raw data is demosaiced a WB profile is applied to the raw data, but there is no WB information contained in the actual raw data that was read out from the sensor. Whatever WB was selected in the camera at the time the photo was taken has absolutely no effect on the readout from the sensor data, it is only used to apply a WB to the raw data to produce the thumbnail/preview jpeg image attached to the raw file. It is also included in the file's metadata, but the application you use to open the raw file with may or may not apply the in camera WB setting. Many raw converters ignore the in-camera WB setting and either apply their own default value, apply a value included in a preset created by the user, or apply their own version of Auto WB.