Let me explain the difference I see. The player that has previous knowledge of a module can play through it without problem, so long as the play isn't disruptive. By this, I mean that the player is using foreknowledge at a macro level to chart a path through the adventure instead of engaging with it. I wouldn't have a problem with a player, knowing a door is trapped, declaring a specific action to check the door for traps, for instance. At this point, the door is introduced into the game and the action is reasonable, regardless of the motivation. The action can be adjudicated with the rules, so this knowledge will still be tested by the play loop. On the other hand, if a player draws a sketched map prior to entering the dungeon (frex) and points to a door on the sketch saying, "avoid this door, it's trapped," then we're at the point of the player being disruptive. I'll admit there's a fuzzy line between the two, but, in general, since I'm not looking for "metagaming" if something actually registers with me, it's likely crossing the line.