Everyone looks like they know the choreography. Most of them are just copying the person in front of them.

Confidence in a group is largely copied. Most people in any room are following whoever is in front of them, and the combined effect looks like shared knowledge that nobody actually holds. Feeling like the only one who is lost is the standard experience rather than evidence of being behind.

Ask the obvious question next time instead of nodding along. You will usually discover several people were waiting for somebody to do it. And when you are the one who knows, say so early, because that saves everyone the performance.