Why wouldn't it pressurize above 1 atmosphere? It has a gasket and those latches look like they lock down fairly effectively.
The description above says it has a vent hole in the lid.
If you blocked up that hole, you could indeed raise the pressure above atmosphere. The point is that you shouldn't do that, ever, in a vessel not engineered and certified for the stresses. Basically, you would have created a live bomb, even though it's filled with the fixings for beef stew.