Uhhh... I'm not sure what the question is. If you're asking if that's an error coin, the answer is no. It's just beat up and stained.
One more time this would be considered a damaged coin not an error coin ill catch on as far as the rules go sorry
You are correct, it should weigh 5 grams. Not that much wear or damage is evident, weigh another nickel on the same scale and see what it is.