oh SEGA! - Iizuka confirms a "SONIC Mach 2" and that Sonic Team is not developing it... before the game is officially announced.

[Skullwaker]

Darwinianevolution said:
Maybe when they say mach they mean the speed of sound?

 

That's probably it. It seemed as if it was supposed to be a sequel to a game that already exists (but doesn't, really).

Because typically games don't have single digit numbers in the title if they're not successors.