More info here and in other places:
http://forums.lostlevels.org/viewtopic.php?t=2460
It's taken from the Wii release. The EU Wii version has an official "pie factory" NES Donkey Kong, which is believed to be an "official Nintendo-made ROM hack" rather than an old unreleased prototype or whatnot. In other words, Nintendo hired someone to hack in the pie level to their regular Fami/NES ROM.