I think you have a point, pun intended. I wish I kept the item I found while I was walking around newly broken ground next door that looks identical to this one. I found it in a location where a barn stood many, many years ago which lead me to believe what I had found was a horse shoe nail and this one was to.
You did bring up a good point that it has a rounded shank so maybe not what I had suspected. After some research I found that not only horse shoe nails had square shank, but all nails were square until machine made wire nails entered production in 1890.