Yes, it's easy to confuse what Pentax are doing with what has been done by Olympus and Hasselblad.
In Olympus and Hasselblad, a slight shift in the sensor is used to create extra in-between pixels - so the image resolution and file size increases.
Pentax shift the sensor one whole pixel, so that each pixel can get full RGB colour information. There's no more pixels, but with better colour information for each pixel, resolution goes up with the same file size.
In the K3ii, the camera takes four 24mp images, then interpolates that down to a single 24mp full colour image. Of course, if Pentax were Sigma, they'd be calling the K3ii a 96mp camera
As for black and white, one can imagine that having more information for each pixel would benefit the final image in some way. All those pixel shift owners out there have some testing to do!