Sourdough Buns Baking Timelapse - From Pancake to Superb unexpected Ovenspring

Those are my sourdough buns baking as a timelapse. They were super flat when I placed them in the oven, but then they just exploded with unexpected ovenspring. The buns have around 67% hydration. I let them ferment for 7 hours at room temperature, then another 2 hours proofing on the baking tray.