A rear wheel from a truck that is driving at highway speeds can have enough force to inflict a lot of damage. If a smaller vehicle was driving down the road, things might not have ended so easily. In the case of a motorcyclist or pedestrian, it would have resulted in death or severe injury.
As you can observe in the videos below, but also in the photo gallery, the windshield of the Explorer cracked, but its inner foils managed to keep it in one piece instead of having it break into thousands of shards.
That is thanks to a breakthrough achieved decades ago, in the form of glass lamination for automotive windows, and modern vehicles feature stronger glass than ever before.
The two police officers in the vehicle were lucky, as a different angle or pitch could have sent the wheel in the passenger compartment. Even with a laminated windshield, things would not have been so easy if it could not manage to keep the object outside the vehicle.
Bodycam footage from the driver of the Ford Explorer showed that the police officers inside the vehicle did not panic after getting struck by a runaway wheel, which is expected of them since they are trained law enforcement professionals, but they are still human, so their level of calm remains impressive.