Actually the DSTwo runs GBA games just fine. I think you might be thinking of this
http://gbatemp.net/threads/gbaemu4ds-gba-emulator-for-ds-i-dsi-entry.281715/
You can't compare an android phone with
System Chip: Qualcomm Snapdragon 600 APQ8064T
Processor: Quad core, 1900 MHz, Krait 300
Graphics processor: Adreno 320
System memory: 2048 MB RAM
To the Supercard DSTwo with a CPU of like 396MHz and 32MB of RAM as well it doesn't use the DS's hardware for GBA emulation, so there's no extra CPU nor RAM from the DS to help with the emulation. But the DSTwo was pretty much made for GBA emulation though.