Are questions of realism on topic? Is it on topic to ask whether Dwarf Fortress represents metallurgy correctly, or whether Call of Duty illustrates the firing of a certain firearm correctly?
Example: Is bronze really better than iron?
Despite our conclusion being mostly the same, I'm going to somewhat disagree with tzenes here. I think your example question about the metals is actually a perfect illustration of the kind of "realism" questions that are appropriate.
Questions like the origins of Super Mario Bros. 2 or the name of Mega Man aren't "realism", rather, they're fact-finding questions centered on gaming trivia. Fact-finding is one of the two elements that the Stack Exchange engine supports rather well, alongside problem solving. They actually have little to do with realism.
But actual realism questions are also fact-finding questions. The importance then is tying it to the game. Just asking how certain firearms operate in the real world is going to be off-topic. Framing it such that you're trying to figure out if a particular game renders it realistically is a bit more on-topic, but a better question would probably be about asking about how the game handles its firearms in general. If it happens to be inconsistent for that game (pistols are done perfectly but rifles have no recoil), a good answer would even cover that information, so it's basically a win-win scenario.
We probably won't get all that many of these questions, but even then they still fit with our system. As long as the question is a reasonable one and rooted in a game, then I believe it is on-topic. An unreasonable question would be one where you can either strip the "in real life" part of the question and it becomes a meaningless question to ask, or a question where stripping the relation to the game doesn't actually change the real question.
I think that question is a bad example because it asks both "what is the state in game" as well as "is this true IRL."
Certainly I could see where a realism question could be bad:
Are Hedgehogs very fast creatures IRL?
But I even in that case I think we can support these question.
If we're willing to support questions such as: Why was the gameplay of Super Mario Bros. 2 so different or What is the Etymology of Mega Man?; neither of which is actually necessary information to play the game but instead is information on the game's background; then I think we can safely support questions about the differences between games' physic systems and the real world.