Assuming that the GPL is fully representative of Stallman's views, they would not be be required to release 3d models, scenes, or the screenplay. Those parts would not be considered software. However, I am not sure about the source code involved in the movie. He makes a distinction between art and software because software is meant to do "practical jobs" whereas art is not so he does not put the free requirement on them.
> Assuming that the GPL is fully representative of Stallman's views,
What does Stallman or his views have to do with it? The GPL is a document that is interpreted by judges and juries, not by Stallman.
The text of the GPL itself makes no distinction between software or other things that can be copyrighted. GPLv3 even changes its language to make it clearer that it can be applied to non-software things. For example, it defines "source code" as "the preferred form of the work for making modifications to it". What this actually means is up to the aforementioned judges and juries, but for a movie, it's conceivable that the preferred source for modification is indeed the 3d models, the original reels, and so forth.
Seeing as he wrote the first version, was involved in the updates, and spends a lot of time promoting GPL, I would assume his views have a large influence in how it is used and perceived. GPL mentions software quite a few times and the preamble states "licenses for most software and other practical works". As I mentioned above, Stallman does not consider art as a practical work.
However, I am not sure how a judge or a lawyer would interpret the word practical work.
The GPL refers to the use of software, the licensing, the linking thereof.
This is nothing that would ever be covered or considered to be covered by the license. It's a screen shot of source code.
I don't think - well I know he's not - entitled to acknowledgement either, any more than the producers of a movie would be required to acknowledge the NYT because one of the characters is reading it in a coffee store.
http://www.gnu.org/philosophy/funding-art-vs-funding-softwar...
Note: I only have a superficial understanding of GPL and Stallman's views.