The OED has sky pilot from 1883. The first citation is from George W. Peck’s Peck’s Bad Boy and His Pa, a compilation of Peck’s newspaper articles that featured his “Bad Boy” character, a mischievous lad who liked to play tricks on his father, sort of a nineteenth-century Dennis the Menace.
but in what way is someone who just flies an ordinary aeroplane not a ‘sky’ pilot
Strange and illogical are the ways of language. Even if sky pilot had been coined after the advent of aviation, there is no reason why this particular construction could not have a narrow meaning. We don’t use gunman to describe a police officer, for instance.