Board Thread:General Discussion/@comment-120883-20150526005118/@comment-1986314-20150526012242

The Sonic canon has always had contradictions. The moon was somehow pieced back together after the events of Adventure 2. Blaze is established as a character from an alternate universe in Rush, only for that to be sort of retconned when she is in inhabitant in the future during the events of ''2006'. In fact, 2006 is one huge contradiction thanks to time travel being used as a plot device.

In this case, humans just phased into the universe with no real explanation, as far as I know. I don't think Sonic's world was explicitly called "earth", but human life is indeed present.