Thanks. This is a novel explanation to me. So to rephrase, some volume of air (~1,2 kg/m³ at sea level) is “plasmarized” and then eats the X-rays, upon which it expands in a shockwave.

It is usually stated, however, that the X-rays go first, and at the speed of light. Plasmarization, OTOH, would be subject to some inertia, however little, wouldn't it. So there'd be a delay before plasma formation, and the X-rays would already be “over the horizon” (joke – they wouldn't follow Earth's curvature, would they).