A lot of early jump & run games worked on a screen-by-screen basis (Prince of Persia, Lode Runner, etc) rather than actually having smooth, NES-style scrolling.

In any case, this Wikipedia article [1] backs up that the only real predecessors of Keen on PC were early-80s console ports that were extremely limited in other ways, like having boxy, low color count graphics.

[1]: https://en.wikipedia.org/wiki/Side-scrolling_video_game#IBM_...