It's a GBA emulator from 2004 by Nintendo, it has nothing to do with the GBP. Nintendo originally used it in those display demos used in stores for Mario vs. DK, however it was later revealed that the same emulator with slightly different settings was released alongside 6 or so Naruto games by TOMY as a reward to tournament winners. Then there's Pokémon Box which also seems to use a the same emu but with different settings.
It is faster than all homebrew emulators but doesn't save; using it in Nintendont lets you use Wii's entire CPU so any game with slowdowns is now fullspeed or very close to it, however every revision has a common problem: emulation freezes randomly and quickly.
The opening.bnr has "AGB Emulator" on it. Even if it doesn't save though it's useful for two things: 1. Some games do not actually need saving to be played and 2. It serves as a very good proof of concept that the Wii can indeed play GBA at fullspeed.
EDIT: It also displays square pixels correctly, something all the homebrew emulators lack.