That is what wheel flop is! (I doubt Jobst would have written something so plainly wrong.)
Actually, you can easily steer a bike while walking with it by grabbing the saddle. As long as the front wheel is pointed fwd the bike will continue in that direction..... To change its direction you simply tilt the bike in that direction. At walking speed front wheel gyroscopic effects are not in play.
Cheers, Nor in Iowa