That tiny island is part of Skyloft, and the dismounting of Loftwings work differently there than in the rest of the sky. Trying to zoom over it and diving exactly on it will always result in you landing on the side of the lake.
I have not reached that part of the game yet, but it would seem it's the island that's a good bit high. Since there are vines coming down from it, I would think that it would be possible to clawshot the vine and be pulled up there as it was possible in Twilight Princess. I however don't if it's possible in this game, nor when exactly you get the clawshot, but my guess is that is the way to glory.