Window cracking isn't uncommon. Cockpit windows are typically made of layers of acrylic glass sandwiched together, with heating elements in the middle. They are exposed to incredible forces, the forward airflow on the outside, positive pressure from the inside, cold on the outside and warmer on the inside, then there's the internal temp when the anti icing elements are on. And despite all of this, they're so strong that a crack can be discovered on one side and the aircraft can still be safely landed.