To be able to make that work, they would have needed about a 6" bench vise, but that would mean the opposite side of the flashgun rim where the batteries go in would also be dinged up/crushed as well. I'm inclined to think a hammer was employed on the bottom because if a vise was used it would not only crush the bottom side but also the opposite twist/lock side and deform it to where it might not fit into the clamp correctly. As you can see in the photos of the Elstree hilt, the bottom tube fits perfectly into the clamp.ie the base against one jaw the other end against the opposite jaw.
Also, you will notice the end of the Elstree hilt is dented on mainly one side of the bottom, and you can see how the tube towards the end is bowed outward at just the spot where the dings are located which in my mind seems to elude to the use of a blunt object. A framing, waffle faced hammer could not only leave the dings/jagged surface behind but would be able to deliver a blow causing the bowed out metal deformation in just that spot on the hilt. What do you all think?