We see finn freeze ,in shock and it cuts to a flash back . Is he remembering ,or is it just showing us the audience. He blocked these memories from early age probably as a baby right In the vault he experienced trauma at an early age and then mentally blocked it and then became afraid of the ocean because subconsciously is associating with past traumatic experience and subconsciously aware of so. most likely. Could him going back to the island and hearing about his mom trigger his memories ,is he able to mentally handle his memories that he blocked for so long ? It seems .he blocked other memories he had to face head on as well. He’s mentally strong now but wasn’t as a baby so he had to block it. Did he learn about his past that would explain why he didn’t learn about his past and, we only did cause it wasn’t only us , he learned when we did . But was that scene only a revelation intended for the audience ,or was it Finn as well recalling his past, or is it up to interpretation?