Did Israel have a real choice to accept or reject Jesus' kingdom?
Yes. Israel had absolute freedom to accept Him and have the kingdom, but also the free will to reject it. God's sovereignty and foreknowledge did not take away that free will; their response, "you would not," showed they rejected the offered King and kingdom.
Les teaches that God in His sovereignty is in control of everything, yet He never takes away the free will of men and nations. Before He ever created anything, the Godhead could look down through the eons of time and knew exactly what every person in every nation would do; that is foreknowledge. With foreknowledge He could plan for any contingency, but He still never took away mankind's free will. Les applies this directly to Israel: Israel had absolute freedom to accept Him and have the kingdom, but also the free will to reject it. The offer went out that He was their King and was ready to give them the Kingdom if they would simply believe, yet He says, "You would not." Their rejection did not throw God a curve, because He knew what they would do.