The weight is within tolerance. Not struck on Dime Stock. They are usually in the low 4.3 - 4.1 grams Here are 2 examples from my collection..
The copper core on a clad coin is not necessarily in the dead center of the "sandwich." It can be on either end, and still have the copper-nickel part on the face of the coin. In this case the clad strip may have been a little thin which accounts for the lighter weight. I don't think that this an error coin.