I think he as Archaeologist has done years of research before finding anything on the island
but he wont say much to others, one: some steal the work of others, two: he needs to find the orbs cause he is not aware they only accept him

but yes, I see it possible that there are more ruins scattered across the island
perhaps, well since I see most of the orbs on this island I am pretty sure, the lost race that made the ruins were his ancestors

oh yeah, since he researched that first ruin where the silver was hidden, he might have found something about the island by that

off course the chance is that a "college" was keeping his eyes on Alexis, thinking that Alexis was on to something and followed him secretly, or planted a bug on the boat.