Have fun with the physics.
I wasn't replying directly to you., Noble.
I'm just providing a different view of why such big prints might exist, regardless of what camera was used. Prints of that size can indeed be made from a small negative. I've seen it done, and it sold. It was a photograph of Mount Everest from a fly-by, using 35mm Tri-X. Printed by Pete Spilde at the now defunct ImageTech Solutions in Minneapolis. 4x5 feet. The buyer thought it was good enough, and I thought it came out really well. Probably couldn't have done that with an 8x10.