Firefly was not cancelled under terms by which the movie got to be made. Not at all.
I don't think that's what he meant. What he is referring to is the fact that, when the film rights to the franchise were sold to Universal, the legal situation was one in which the series couldn't be made on television again for (IIRC) ten years, essentially rendering any televised versions of Firefly dead. I'm not sure exactly how or why the deal went down the way it did, but that's as best as I can remember it.