And there's a limit to what you need to look up in a book. The limit moves further up the more you work with a certain kind of tool or study a certain kind of knowledge. I have to look up trigonometry every single time I need it because I only use it sparingly. I don't need to look up SLD-Resolution, which is my main subject. How much would Feynman need to look up when debating physics?

So when someone like Feynman talks about physics, you listen carefully because you know they know their shit and a certain kind of nerd deeply appreciates deep knowledge. When someone elbows themselves in the limelight and demands everyone treats them as an expert, but they don't know the basics, what do you conclude? I conclude that they're pretending to know a bunch of stuff they don't know.

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[1] ... some do. But they're students so it's OK, they're just excited to have learned so much and don't yet know how much they don't. You explain the mistake, point them to the book, and move on.