Excuse to make knife sharpenable for "average" customer is very popular.
Everything you do less than optimal tends to make the steel softer, however lot of people will promote softening steels to make them easier to sharpen so it isn't a problem unique to Stewart. He is just using a well known "fact". Stewart's customers tend to be willing to believe anything he says without any proof and he takes advatange of that which isn't surprising.
For a long time he said he was hardening A2 for "maximum grain growth" which shows a complete lack of understanding of heat treatement of steel on a basic level as grain growth is a negative. It makes steels more brittle while they are weaker. I noted that was a glaring problem and he changed it but he still has the temper/cryo description inverted.
Cryogenics is for converting retained austenite and inducing carbide precipitation, it is not for stress relief. In fact cold treatments actually put the steel under stress by forming untempered martensite which is why they have to be tempered after the cold treatment. Tempering is specifically for stress relief, that is why you do it because as untempered martensite is so stressed it can crack on its own. It can even crack during the hardening if you do it too quickly.
Grain refinement comes mainly in the preperation before the heat treatment, the rolling by the mill. The grain of the steel can also be blown in hardening but generally not refined unless you are using the word to mean something different than the standard materials defination or you run normalization cycling for some reason instead of the mill.
He also promoted A2 as being very expensive to work/buy which is no one used it. Again, shenannigans. It is common to use very high carbide steels in modern cutlery which are harder to grind, and more expensive to buy, heat treat and grind.
Regardless of all of that, the steel and geometry are much more coherent with the promoted tasks of the knives than a lot of cutlery which often have all elements of the design in contradiction. A2 is a nice steel for a wood craft knife and is designed to work in acute edges because it has a low volume of very small carbides, similar to AEB-L and other steels.
-Cliff
