knowing what will happen does not mean that he prevents or causes that thing to happen. The sun will rise tomorrow. I am not causing it to rise nor am I preventing it from rising by knowing that it will happen.
Likewise, if you put a bowl of ice-cream and a cup of tea in front of a small kid, you know for a fact which one is chosen, the ice cream. You knowing it ahead of time did not restrict the kid from making a free choice when the time came to make a decision.