Since Adventure, I always assumed Sonic propelled himself forward by spinning mid-air a lot quicker than usual for a bit, and uncurling as a result of not hitting/targeting anything. Adventure also shows somewhat that the animals sort of do have some kind of protection from the affects of the badnik destruction (that green orb/shell around them).
Perhaps this is possible because Sonic & co are actually flipping forward/backward. This is especially reinforced by the jump animations in SA2.
Quoted For Truth. To reinforce this, take a look at the original Big Arms boss. This is the first boss to damage Super Sonic, via literally body slamming the rings out of Sonic directly. Being caught mid spin by robot hands would also certainly catch Sonic off-guard.
Kinda been explained already how the impact of the Death Egg caused the Island to fall into the sea. After Sonic's story, the island is restored to the skies as seen in a cutscene. Then Knuckles' story takes place which, and the end of it, you can see the island still in the sky, just very wobbly. Doesn't quite explain why the edges of the island are sandy if they're not usually by the sea though...
Here, one could assume that Angel Island was not always airborne, and thus has always had sandy edges from when it was submerged long-term. The other option, is to assume that Sonic and Tails actually landed and entered Angel Island through a very large bay or lake.
Maybe because both Sonic Team and the characters themselves are trying to forget that god awful game ever existed?
Hilariously, I always thought of that as a "let's not ever talk about this" thing among the cast.