This is pure speculation, but there may be a PID, thermometer, on this oven. At the lid removal, there is a brief glance at a small gauge electric wire coming out of the top, a bit to the right. It would be too light to power a blower, but it appears the heat source comes in from the bottom anyway? Definitely, I do not dispute judging temp through experience, the crucible though seems to hover in the lower red, medium red spectrum? The crucible never seems really bright to my eye, the way part of the oven interior appear.
The thing that always is interesting to me is the delay from oven removal to quench, either counted off or part of the circumstance of walking the crucible out of the shop. I think there is a cut in the video, but it appears to be a continuous process that likely takes fifteen to twenty seconds from the oven to the quench. Particularly with the lid off, the parts are likely cooler than whatever temp they soaked at, in the oven. I have always wonderered if that was one of the tricks to low distortion, quenching games to catch the parts cooler than the nonmagnetic point on the way up? An edge to center of mass temp difference might also help with his color distribution control, ending up with those classic islands of blue framed by paler colors.