Hey there!
Welcome!
I'm sure this forum will be really helpful!
I once knew a 3rd generation American-Japanese guy, too.
He came here to Japan to be an English teacher. He couldn't speak Japanese at all although he obviously looked Japanese, so many people thought he must be Chinese or something.
When we went somewhere together, Japanese people got REALLY confused.
Why?
Because naturally they turned to him and talked to him only, ingoring me (the foreigner).
He couldn't understand a word, so I answered in fluent Japanese.
You should have seen their faces! *LOL* ....
Oh, Japan! *g*