That's an interesting twist, I wasn't aware. To be honest, I don't have the most reliable source: I heard the term "uncle Jokes" first from an episode of Teen Titans Go [1], which my kids love. Also after you watch a few episodes it grows on you as a pretty good bit of satire. Or I'm suffering Stockholm Syndrome.
[1] https://m.youtube.com/watch%3Fv%3DCz9WpuIcUPk&ved=2ahUKEwiMl...