We haven't seen the whole flashback so I don't know how he feels about Al kamar, but with his meeting with Tenkyu and how he phrased his insecurity, maybe he feels like he's more like them. Sakamoto talking about where he belongs also feels related to his origin and where he chooses to go

#SAKADAYS200 I was rereading skmt to see the references to de Al kamar theory and just found this one that now makes much more sense. When we learn about the orphanage the first time I didn't remember Shin reacting, but now I think Shin has been putting things together since then.