The MSF courses by me list that as a prerequisite for the classes.
But I think it’s mostly because if you’ve ridden a bicycle, you’ll be familar with how a two-wheeled vehicle handles and moves (and doesn’t, as the case may be). The classes will teach you the mechanics of riding a motorycle (how to use the throttle, how to turn, etc.), but they don’t teach you the mechanics of how a two-wheeled vehicle operates….they assume you know.
So yeah, get an inexpensive bicycle and learn to ride on that first…will make learning to ride a motorcycle much easier (every bit helps, as there’s A LOT to learn).
And there are no stupid questions here, so ask away to your hearts content!