Iron pontil is the same thing as graphite. I think most people consider "iron" or "improved" pontil to be the correct term but many people call it a "graphite" pontil as well. You see those little nipples on iron pontil and open pontil bottle bases as well as some smooth bases and I would imagine it is a centering mark for when they machined the mold.
Despite auction attribution (often wrong when describing an unusual bottle), I still think the bottle could be French. The fact that collectors are reluctant to bid on these bottles (two bids in the 2003 auction) tells me collectors don't trust this bottle to be American-made.
I don't have this prejudice. I think it's an interesting bottle, and would be happy to put it on my shelf.