There are two issues here. The 1st isn't metagaming, it's the reading of books at the table and possibly being disruptive of the game as a whole. I've dealt with this above.
I'm sorry but no, it's not necessarily reading book at the table, and I was specific about the type of disruption.
The second is on topic -- if the PC is doing a thing then it's because the PC knows it. The question isn't one of OOC or IC knowledge. This is a prime opportunity to invite the player to tell the table how their PC knows things, which, last I checked, kinda falls into the usual definitions of roleplaying. Doing this cannot ever be a case of not "recognizing" other characters.
It does, because the explanations - when they exist, usually it's a quick retractation based on "Oh, I shouldn't have said that" because the player realises that there is no way his character could have known something that specific - are usually really bland and leave everyone else at the table with their eyes rolling, which does not add to the game.
Oh, goodness. I mean, let's say I'm the most tactical minded player at my table -- how do I restrict this OOC knowledge from being powergaming?! This is one of those arguments that seems like it lands until you consider the host of other things that are perfectly acceptable that have larger impacts than knowing trolls are weak to fire. Skill at PC builds. Synergies with other characters. Tactical acumen. All of these things do exactly the same thing you're complaining about here, but somehow these all get a pass while you have to absolutely pretend you don't know about trolls (example) to prevent unfairness or unevenness in player performance.
And again you should know, from other discussions that all these others do NOT get a pass either (and in particular the horrid "skill at PC builds"), so that is a really weak argument.
But you are right, it's always the same type of people who claim that they are very clever at technical building of characters, technical synergies, monster knowledge to use with these builds and synergies, and who of course claim that they are masters at battlefield tactics, even if their character is just a youngster green around the ears. I don't need to spell it for you, do I ?
And it's funny how, in the end, the excuse for letting powergaming behaviour get a pass is everytime because there might be other ways for a powergamer to powergame. No, there is no "excuse" (and there should not be the need for one, if it's your preferred playstyle, it's fine as long as it's not imposed on others, in particular by stealth), and each of these points can be addressed on its own.
And this is why at our tables we act all across the board to limit these, the "monster knowledge" (although you might have seen from another post that we are pretty lenient about those) is just a facet of limiting these effects. No inconsistency there.