You are talking about the energy of the blast. In my comment I was talking about the heat output. From the followup comments it seems I have not made it sufficiently clear.

The energy of the detonation wave in rocket explosions is typically 1-2% of the energy in the fuel, at least that is the ballpark of what people use for estimating the effects of mishaps.

We also do not know if the tanks were fully filled -- it the past, rocket companies have called 10 second static fire tests a "full duration static fire test." We will probably find out later what it actually was meant to be.