Most blades are heat-treated in an oven which results in a more-or-less even hardness throughout the blade.
Differential heat treatment, which results in the so-called "hammon line(s)" that you've observed, is accomplished either by selective heating often with a torch, or by shielding part of the blade from the heat by covering it with an insulating material. Clay is often used and so you often hear this described as "clay tempering."
The gentleman you're referring to, I suspect, is Paul Bos. He is quite famous for achieving excellent heat treating results. What's magic about his process? Well, nothing except that he's got it all dialed in and he's very experienced with it. He consistently achieves excellent results.
Heat treating is very much science at its core, but in practice it remains very much an art to get everything exactly right to achieve the best possible results consistently.
Heat treatment of many modern alloys is quite touchy. Many modern alloys are quite sensitive to heat treatment. The difference between a great knife and a piece of junk can be just a few percentage points on a temperature or a time. So, to achieve excellent results, you have to have your process well-controlled.
Such carefully-controlled processes require expensive equipment and also a lot experience and experimentation. Most small-scale knife makers choose not to invest either the money or the time and, instead, look to an outside service. Mr. Bos has been offering that service for some time and is famous for delivering consistently-excellent results.