The example seems to me to be an example of sly wit rather than a malapropism -- that is, a verbal contract obviously isn't written on paper, so the value of that non-piece of paper is nothing, which means that a verbal contract is less than nothing... the exact point Goldwyn was apparently trying to make.
You never were sure with Goldwyn.
One of my favorites of his was, "Well, if it comes to that, include me out."
I don’t think Samuel Goldwyn had a ‘sly wit’. I don’t think the ‘verbal contract...written’ confusion was intentional. I remember a story about Samuel Goldwyn meeting with his production people discussing the then current run of religiously themed movies like ‘The Robe’ they were making.
Samuel Goldwyn was trying to make a point about the ignorance of religion among them. Supposed he said, “I’ll bet $50 that no one here even knows the Lord’s Prayer.” Someone recites ‘now I lay me down to sleep, the Lord I pray...’
Goldwyn throws down $50 saying, “Damn, I didn’t think anyone knew it.”