It was something like that the app must have been "originally written" in certain approved programming languages. It basically targeted cross-compilation, but it was written so vaguely that on paper it appeared to even disallow native iOS apps if they started out as a port from some other language.

There was briefly a kerfuffle about it, as people using other cross-compilation tools (xamarin? etc) worried their apps would get removed as well. But IIRC apple never actually enforced the clause, other than to remove existing flash-based apps and reject new ones.