Don't beat yourself up. You were in a no-win scenario. Honestly, the best option might have been to go COMPLETELY off script. Admit to your audience that they know more than you about the core subject. Just give that to them. Then talk about why you find the subject interesting, and how it relates to your work. Maybe even open it up to a Q&A with the expectation that you'll look kinda dumb but learn a lot.
Of course, I've stayed far away from academia, so what do I know.