Artificial high-pressure is built up in the oven due to the heat. When you open the door, the high-pressure air immediately rushes towards areas of lower pressure (the rest of the kitchen) and you get the brief “wind”. Same thing happens meterologically, but on a global scale.

awaiting the thump on the head from those who know LOTS more

Don’t underestimate the force of free convection from the 800 degree R air in your oven mixing with the 530 degree R air in your kitchen. Especially when you first open the oven, and the air has a small area to flow through, and thus has a higher velocity.

No, or else you would likely not have free convection occuring even.

Free convection happens when you have a fluid which has density gradients. This results in a buoyancy force which causes the free convection to occur. Since the density of the air is directly tied to the temperature, the greater the temperature differential, the greater the density gradient, and thus the greater the buoyancy force.

The temperature differential terms are normally expressed or contained within a dimensionless parameter called the Grashof Number. But I won’t go into that, as we need to start talking partial differential equations to fully understand where it comes from.