So if we add "or the player just plumb forgot" then we can discuss something more productive?
Hey nobody is forcing you to discuss this. You jumped in. I think this is plenty productive. If there are many examples which cause you to add an exemption, eventually you'll realize your general rule was flawed and needs to be altered. That is...if you're arguing in good faith.
It seems to me that some people can see the difference between "metagaming" and bad faith play and others, perhaps those who generally have a dim view of "metagaming," cannot. It costs me nothing to just add qualifiers to a claim I didn't make, so deal?
1. A player reads the adventure and decides to not disclose this the DM - this one is the only clear bad faith one.
2. A player simply sees a single spoiler somewhere but decides to not disclose this to the DM because they are worried it would rock the boat and think a single spoiler is no big deal
3. A player see a spoiler and forgets to tell the DM but meant to
4. A player sees a spoiler and forgets to tell the DM but then remembers mid-game but chooses to not disclose to the DM in the moment because they feel it would harm the game to disrupt it with this conversation
5. A player sees a spoiler but didn't even realize it was a spoiler at the time until they see the creature in question and then doesn't disclose because it would be too big a fuss or disruptive.
I can keep going. Not all metagaming that's a player's "fault" or which is "neutral" is bad faith.
It does cost you to keep adding qualifiers - because too many makes it useless as a statement.
Which is what it is - useless. Not all metagaming is the DMs fault. Sometimes it's the players fault. And sometimes it's nobodies fault. And sometimes metagaming can be good. And sometimes it can be bad. And sometimes it's really not good or bad. Which is how most things in life tend to go - non-absolutist.