That's an interesting observation. Removing a LOT of material around the pivot to incorporate the internal stop pin appears to be a fairly common practice. Here's a borrowed picture of a Spyderco Southard blade for comparison. As you can see, the Southard also employs an internal stop pin:
It's also worth noting that the plunge lines on both the Southard and the Hi Jinx come extremely close to the stop pin cutouts when their blades are fully deployed. A Southard blade failed at this precise location for reasons which have yet to be determined. The obvious question is whether the proximity of the plunge line to the stop pin cutout creates a weak area in the blade.