I am going to stick my neck out here and disagree with both. A corn is a bruise caused by inappropriate/too much pressure. I've seen corns in both shod and barefoot horses.
Mostly the bars have overlaid onto the sole and the resulting pressure has caused a bruise which is often not spotted until the offending bar is removed or wears off.
I have also seen a very tall foot where the bar hasn't overlaid as such, there are layers of false sole in the way. But the bar has also grown equally tall and pressed against the sole in the vertical as well as the horizontal planes.
|Corn day one|
|4/5 months later|
Note the improved quality of the frog.