Correct the misunderstanding at the point where it began, not after everyone has acted on it.

Errors get more expensive the further they travel. A wrong assumption caught in the meeting costs one sentence; the same assumption caught after three people have built on it costs a week and some embarrassment for everyone involved. What delays the correction is usually social rather than practical: interrupting feels rude, and you are not completely certain, and it might resolve itself. It almost never resolves itself.

Say something the moment you think a room is working from something false. Phrase it as a question if that makes it easier: can I check what we mean by that. Ten awkward seconds now removes a great deal of work later.