I doubt this is real, cause since 2007 there was never any official release for this game on DS, only on the Wii. Nintendo official site only shows the Wii version for this title. If it's a port of the older gen console, then the file size strikes me as odd. Unless...., this is a fan-made version using NSMB tool.
Of cause, it's fake like I said in my earlier post. Never was any of that 'galaxy ds' version for Mario since 2007. There's also the 'sunshine ds' vesion too.....fake as well. Check Wikipedia if you want to see the complete legit Mario Bros releases for all consoles.