Question about Dr. Choi

-Possible spoilers-

After Dr Choi and Sun-Joo have arrived to that island where Eun-suh grew up, there's one scene where Dr Choi is standing at a cliff viewing the sea. Than he turns around and sees a little child version of Eun-suh walking into the forest and he starts to follow her.

Then later on in another scene, Dr Choi tells Sun-joo that he "found out something interesting". So I'm wondering; what did he found out after following the little girl?

I was thinking that perhaps she showed him her house where she grew up in because Dr Choi seemed to know where Eun-suh's house where when he and sun-joo decided to search through it. But that doesn't really make any sense. I mean Eun-suh's relatives could have told them were her house where and if not, why would Eun-suh even bother to show him her house?