I remember speaking to Fred shortly after the document refered to in the above post was published.
Whirls, sitting in the left hand seat aside, I believe it stems from the fact you don't sign for the aircraft when doing the Traffic watch or Boat Picture taking ergo your are not PIC.
Chester2005 I take it from the OP's post that he doesn't hold an FAA CPL(H) and even if he did the point I made out to Whirls above would apply.