That was speculation showing that God if He had known she would refuse He would have still acted in history to save us. Even if not by that means.
Would you say that Mary was predestined to be the mother of Christ ?
If we look at the necessary requirements for the Savior to fulfill the OT prophecy, He had to have a specific lineage which He had through Mary and her husband Joseph.. His father by adoption ...The bible says that when the time was right (Gal4:4) He sent His son ..So the timing of Christ's arrival was to coincide with a system of roads and transportation that would allow for the gospel to spread..
So the mother and fathers existence had to coincide with the right political environment
Was all this happenstance?