I don't think Kakashi himself gained access to PS, he simply copied what he observed from either Sasuke or Madara. We've seen him perform elements/jutsu he himself couldn't do, we're able to copy it precisely.
Therefore, somehow I think this is copy, as him being the "copy ninja" was emphasized so much this chapter.
Therefore, somehow I think this is copy, as him being the "copy ninja" was emphasized so much this chapter.