For those who don't have these items to compare, I've taken a picture to illustrate the point. I apologies if they aren't as clear as the naked eye, but I did my best.
This is a true rifling on a pistol where you can see the raised portion, or positive deflection of material that makes the grooves, on the lip of the barrel.
If you ran your finger nail on the inside your finger nail would catch on the positive/up-ward deflection of material (aka peak).
This is a picture of a HH goldmember where from the "rifling" of the barrel is made by removing material. It's harder to see from the picture, but if you ran your fingernail along the inside you could feel that it catches on the channels created by the removal of material from the barrels cylinder during manufacturing. The milled away channels are the darker tone channels, while the channels that have horizontal brush/milling marks are the base level material. Your finger nail catches on the junction of the two channels (peak & valley) where material was removed from the neighboring channel. Another way to say is that these channels are created because material was removed (aka valley), while a rifle/pistol has riffling because their is a raised portion of material that create the barrel twists. I hope this makes sense, if not....sorry I tried.
I looked on HH website to see if they stated how they machined their barrels, but wasn't able to see where they mention how they create the twists of the barrel.
These theories can be debated, which they have extensively on other threads, but for me the proof is in the pudding. I have several HH barrels and love them. They shoot great, but do take a little adjusting of fps with the velocity to find the so called "sweet spot." My two cents is try one and see for yourself, I find that most of the negative or pessimistic views come from those who don't even own one.