I doubt he didn't but it's not entirely implausible to think that he didn't. Completely removing Bethesda from your mind you can still gather some evidence he could be lying. The chosen one has a dialogue option to call out his story on how he invented jet to be bullshit. I still doubt he didn't invent it though because what would be the point in testing on all those slaves if that's not how it works? I don't know. How do you personally reason that he did or did not invent jet?