Riding a bicycle presupposes movement and control. To accomplish the act of riding a bicycle you must be able to steer otherwise you will just fall over to the side and you will not be riding it anymore =)
Your link was about what's needed for bicycle to be self-stable. That steering is required to avoid falling over (as opposed to, say, keeping balance by shifting your weight slightly to one side or the other as needed) is an experimental result and not baked into definition of "not having a steering wheel", even if it is a physical consequence of not having it.
No, not by definition.