I can’t tell if this is simply fat or mold. Anyone have an idea?
I don't think it is fat. I think it is sinew. I make jerky pretty often and even fresh jerky tends to have some white streaks from connective tissue; they don't really absorb the marinade and stay white. And the tiny bit of fat that melts out can also be white if you refrigerate your jerky, but that normally looks more like droplets.
That said, I can't tell how it smells or tastes over the Internet, so as stated in most questions of this nature, better safe than sorry.