Replying to Jordan Peele’s “Us” *spoiler don’t click

Alright I just left the theatre so don’t read any further if you haven’t seen the movie.. does anyone believe that the boy who lived at the end of the film was also one of the tethered? Was he switched out the previous summer? He was saying phrases the family never heard him say and pointed that out, he was building tunnels instead of sandcastles, forgot the magic trick he once knew also was not killed by red as she took him into the basement of the underground base because she knew that was her real son she birthed down there and taught him english? What are your thoughts?