How can this driver power a high-Side MOSFET?
This particular device simply performs the logic level translation and isolation for you. It does not do the floating supply generation.

As your second quote indicates, you need to supply the driver side with the right voltage supply in order for it to function as you expect it to. That means, if you want to drive high side N-Channel MOSFETS you need to provide your own floating supply circuit that generates the appropriate voltages between GND2 and Vdd2.