I think rather than "radiant energy" the dutch oven (being pre-heated) acts like a "thermal capacitor" because of its mass. It discharges a large amount of heat

I think rather than "radiant energy" the dutch oven (being pre-heated) acts like a "thermal capacitor" because of its mass. It discharges a large amount of heat into the dough very quickly once its dropped into the confined space. The lid trapping the humidity in that tiny space does the rest.