Hi.....Yes, Pickingill is one of the less common spelling variations; but "the" George Pickingill was after all (apparently) buried as Pettingale and known by a number of other variants during his lifetime as were his father and children. It seems to just be creative spelling, there is no real doubt that Pickingill is a variant of Pettingell.
He is a character who may be of some wider historical significance, that as well as much else is disputed. Tracking his kin would be helpful, it seems that his father was a Charles Frederick P of Canewdon, Essex and possible but unproven that his grandfather was a Thomas P of Canewdon. Before that the family has not so far been traced in EssexOne of the unproven things but fairly likely things said about him is that his family came from Norfolk. Another unproven thing said of him was that he had gypsy kin.
I'm assuming that his family links up with yours somewhere. If it is true that he came from an ancient family of "cunning folk" then other shoots of the family may evidence that as well!