If you look at the bottom pic you'll see a piece of brick holding up the back of the tang. The edge of the blade is resting on the bottom of the forge opening and the blade isn't touching anything else. The flame isn't making direct contact with the blade.
With that set up it doesn't take long to bring a small blade up to its critical temp and there's a lot less risk of overheating the blade than when using a full-sized forge. I'll watch it as it heats up, check it periodically with a magnet when I think it's approaching non-magnetic (calibrates my eye for determining when it reaches critical) then hold it with tongs until it reaches critical, sometimes working the blade through the flame to ensure an even heat.
I've given away dozens of those mini-forges in the last few years... it takes just a few minutes to make one. I'm just about out of bricks now.