Well, we know all of that, but to the island's residents he did appear out of nowhere with no connection to the island, and managed to defeat the lords. And then there was that chapter where they went into Kayruu's dream and Ikuto had a strange sensation. And then in this chapter right as they were talking about who was an eye it cuts to him.
I don't think he actually is one though, it was probably a misdirect and Suzuran is the real eye as you say, but Ikuto definitely has some relation to Kayruu/the island, imo.