Duck!
If you were driving in your car and someone shouted 'duck!', there's a high chance that you would crouch down, thinking that you were about to hit a low-hanging branch or a passer-by was gearing up to throw a burrito at you. But in this case, they'd shout because they were quite literally looking at a duck in the passenger seat of another car! Why? Well, we have absolutely no idea.
In this duck's case, we can only assume that the wild animal was struggling in the midday heat outside in the wild. So, they decided to take themselves off to the nearest car and turn up the AC to cool down.