It’s not about guessing the correct thing to say, it’s about imagining the fictional environment described by the DM as a real place and your character as a real person in it, and using your intuitive understanding of how the word works and how your character thinks and acts to decide what to do in the fictional scenario. What I would call really roleplaying, as opposed to merely acting. And you’ll notice, all three hypothetical players described actions that made sense in the scenario, and all three resulted in useful information. The first player confirmed the metagamer’s suspicion that the symbol was the seal of the dwarf king like he thought. The second player may have gained valuable information about this king, and the third player gained evidence that might suggest the metagamer’s suspicion that the king worked with demons might not be accurate. So you see, the metagamer using knowledge of the published adventure not only didn’t ruin the game, it actually lead play down an interesting path, where characters are taking action and gaining information that may help them form a more complete picture of what’s going on. They are serving the goals of play, having fun and working together to create a memorable story.