Because the game is a standalone executable (EXE) on PC, getting it to run on Android requires a bit of trickery—specifically, an emulator or a wrapper.
Sonic XG is a fan-made love letter to the "Boost Era" of Sonic games (Unleashed, Colors, Generations). It features: Sonic Xg Android Download
Because this is a fan project, you won't find it on mainstream storefronts. To get the most stable version, check the Sonic Retro Forums for the latest links and community-verified Android builds. Because the game is a standalone executable (EXE)