As GG! and Penguins encyclopedia entry states, Flicky was made in 1984 and thus not in the "Sonic" games listing. Plus that Flicky was revived for Sonic The Hedgehog, not vice versa. It's a basic matter of pre-dating the Sonic games totally.
Well, think what you may but according to the holy GHZ bible (GG's information area in the GHZ) the game isn't in the listing. I do admit that the game did kind of have similar gameplay to Flickies Island though so Sega may have looked back at the game as a distant relative.