I think the gallery you describe can still fit with what he’s saying, whether either of us agree with him. I would say that the gallery is not an expression of film as a medium since you’re removing the fundamental components of time and motion from it. It becomes an expression of photography made with unconventional methods, I think.

In the same way that an excellent film score does not necessarily stand alone as an excellent piece of music, a frame from a movie could be absolutely perfect in its role as part of a shot but uninteresting by itself in isolation. The score wasn’t intended to go without the film, just like the frame wasn’t intended to go without the rest of the shot. Maybe they do turn out to be interesting by themselves but it’s at least partly a coincidence if it happens