Bing/Cooperfish Foil

Does anyone know what is meant in the reference to “foil” in regards to the Bing Foil and the Cooperfish Comet?

I know that, “Foil is the change in thickness of a board as you travel from its tip to its tail”. However, it seems as though the use of the term foil is a little different in regard to the Comet and the Bing Foil. On the Cooperfish site Gene states, “the comet is more of a “foil” than any of my longboards”. He uses the term as if it’s a style and not a data point. Does anyone know what he means by this?

Lookin forward to your input.

Thanks

John