I wondered about that too, but Callaway's literature always references the cannon, not Bobby Jones.
I found this in an article in Emory Magazine: "...according to the company's founder, Ely Callaway, "Instead of just calling it `The Cannon,' I remembered from my reference books on World War I artillery this giant cannon on a railroad car called Big Bertha. And I said, We're going to call it Big Bertha."
BB was a big success, but it appears that Ely missed the fairway with that one.