John,
I always thought of a broiler as having ribs, holes and that sort of a pan. Yair, you had to heat sad irons somehow in the old days and the kitchen range was often hot. Your pan has the room for at least three irons and would sit with the heating surface closer to the fire than a pan that was flat across the bottom instead of having a pit bottom. Closer to fire=hotter and faster heating of the irons. OR, you could use the pan as a griddle and I would expect that people would use the pan as they best saw fit. If intended only as a griddle I wonder if the pit bottom was really necessary.
Steve