People have had leaks for Pokemon that have been done similarly.
I've done multiple photo trials with my white 3DS and it doesn't really match up.
I've tested multiple shutter speeds, apertures, ISOs with a few different light sources and things just don't match up from a photography standpoint. If you were to get the photo to fall in sync with the refresh rate, the background would be much darker. There's a lack of bokeh if you were to get the photo to turn up at that exposure, screen glare, etc.
Leaks usually come off a smartphone camera anyway and without the proper apps, it's pretty hard to get it in line with what you want.
If you were to note the lack of HUD and percentages, I guess they relegated that to the touch screen rather than the top screen. If that person thought the same thing, then they would purposely chose not to take a photo of the touch screen because they wouldn't know what it'd look like.
In any case, we can assume unless there are more instances like this it's just an intricate leak. If you were good enough with 3Ds Max modeling and photoshop, it's not impossible to use photos as a reference and rescale and retexture to give it a "Smash 3D" look.