This type of paper shredding happens any time he can find a paper towel or Kleenix. He doesn't care about any other kind of paper.
My girl Fleur does the same thing. It's a mystery to me. They don't seem to want to play with the paper, and they are done with it very quickly!
UPDATE : I was getting ready for bed and heard something tearing...You betcha! Power had found a paper mailing envelope and shredded it. So it is not limited to paper towels and Kleenix!