It's fake as shit.
Those screens it's showing are the EXACT screens taken from tests of the iDeaS emu, which is a work-in-progress DS emulator for PCs. It's pretty damn unlikely that the person doing this "DS-on-PSP" emulator just HAPPENED to take a pic of the Metroid intro at the EXACT SAME FRAME as the iDeaS author did. All this is, is another stupid hoax by someone who is simply using the PSP's picture browser to look at a picture.
Here's the proof:
Here is a pic of this supposed "DS-on-PSP" emulator:
And here is a pic from the website for iDeaS (notice, it's the EXACT same as the one above):
And here is the pic of the supposed emu playing Metroid on the PSP:
And here is the picture of iDeaS that this was stolen from (and again, notice, it's the EXACT same as the one above):
It's bullshit, no need to pay it any mind.
The PSP having the pic viewer makes dumbass fakes like this so easy, it's just stupid. Anyone can pull a hoax, now.