The Japanese Sonic 4: Episode II website refers to it as "the planet where Sonic and his people* live". *The phrase used is ソニックたち, Sonic-tachi: https://www.japanesewithanime.com/2017/08/tachi-meaning-pluralizing-suffixes.html It's not. It's directly from Sonic Team. That's why Iizuka has said so several times over the past 10 years. That's why it's casually mentioned on the JP Sonic Forces website. That's why the IDW comic, which goes through Sega of Japan for approvals, follows the same premise. You're putting way too much stock in a generic background element seen for 3 seconds in a cheapo slideshow cut scene. (The rocket doesn't even fly from that planet, just past it). The world maps in Shadow the Hedgehog, Sonic Unleashed and Sonic Forces are all completely different anyway. Sonic Rivals 2 also explicitly says that Silver is from the future, so it's clear what he means from context. Sonic Forces says Sonic is from another world, with no additional context. That's because, in the current story, he is literally from another world. That's why the Phantom Ruby is a new and unknown thing to the Modern Sonic cast, the events of Sonic Mania didn't happen on their world.