you are completely correct - as I mentioned in the end this would be easier extractor: "Want to relax IID assumptions and avoid careful setup of a non-correlated quantizer? Easy — use any good universal hash function. The only new requirement is that the universal hash will require a one-time seed. We can make an easy assumption that the iPhone local state of /dev/urandom is totally independent from thermal noise camera is seeing, and simply pick that seed from everybody's favorite CSPRNG."
The main reason we went with VN instead of SHA or universal hash is just was more fun thing to build/experiment with. SHA is like flamethrower that will deal with anything you throw at it. VN is far more brittle and you see all mistakes in scenery or generation. Of course then you hash the output anyway before use!