That is an interesting question. I think it is a pump. Yeah, it is a pump. A frame mounted pump. They are removable. I have seen them before. This answers your question?
I have one on my Ribble Audax commuter, my Colnago CT2 (which I swap for a minipump to race), and on my Colnago Superissimo. All of them live under the top tube and are secured with velcro straps. Having a full sized pump when you need one in the back of nowhere is priceless.