What? The diagram is not about how a bike turns, but rather how the vehicle moves when the wheels are rolling and the passenger does nothing: it doesn't fall over if the wheels are rotating at sufficient speed.
What? I saw a bike leaning and turning. The passenger is "doing nothing" because it's just a checkered ball without animation, but that it's not how bikes normally behave (assuming a "passive passenger" as they say), it's pretty obvious that the passenger needs to be shifting its weight to achieve that.
That is just the natural behavior of a bike. Have you ever ridden one? Without using your hand?