Considering Sonic wasn't mentioned as a game that inspired Pixel, I wouldn't consider it a particularly likely source, considering, as many have said, there are a good deal of other islands that exists within video game and anime lore.
Just to name a few, Laputa (mentioned), SKYPIEA, the islands in Skies of Arcadia, and Zeal from Chrono Trigger.
Although in terms of basic concept, Angel island looks the most similar to The Island, but the idea of an island having a power source was used in Laputa, Anglel Island, and probably a few more fictional floating islands.
Not necessarily definitive, but I wouldn't entirely doubt it.
My vote is still on Laputa, though.