does the tread pattern on both tires look the same?
Its not uncommon after a redesign to have different sizes. Most tires seem to be undersized now as the marketing of wider tires are the current trend.
I'd doubt it's a knock off, as the Smart Sam is not a popular tire as I'm aware and couldn't imagine much profit in making a mold to sell a few fake tires.
Post some pictures, might be easier to tell that way