I learned to braze with a torch that's the size of my forearm, so I think your torch setup is fine. You need to learn to move the flame off of the tube when it starts getting too warm. When I'm brazing, I constantly move the flame off of the workpiece. Paul Brodie in that video is mostly aiming his flame at his fixture, and he does the whole operation really quickly. He never really aims the torch at the tube. When you applied the filler, you just left the flame right on that spot on the tube. You can see the tube getting too red very quickly. You want to aim the flame at the thick part of whatever you are brazing and only go out to the thin sections if needed.

There is also a point in the video where you are aiming the flame at the tube past the braze on and the tube behind it gets really hot. The main problem with that is the filler might run out onto the tube. It's really annoying when that happens. You lucked out.