If Mark says he shot the scene, (and unless someone on the film crew comes forward to say otherwise) we just have to take his word for it.

If they had told us it was the severed head from Empire, (made from a cast of Hamill's head.) I would have found that plausible too, as they did use a puppet head of Harrison Ford for the thawing out scene in Jedi.

We're all so keenly aware of the nuts and bolts of the film making process, it's understandable to want to take this scene apart and identify it's component parts.

In the end, no matter how much trivia we know about these films, we have to defer to the people who were actually on the set once in a while.