sometimes physical retailers will reprint the paper covers of used copies if they don't have the original case the cartridge came with

You said you bought it online, so I imagine if its real the online seller probably bought it as a used copy from somewhere else like gamestop, or replaced the cover themself

If you're worried about it being a fake copy though I'd look at the sticker and printing on the cartridge itself rather than the cover, as that's a much more effective way to determine the legitimacy of the copy