He was smiling at the guy he loved like crazy. It was a genuine smile in some ways, a faked one in some other. Namjoon had just asked him if he was alright because his thoughts had wandered off - again - and so Taehyung had smiled and nodded now.
"Of course I'm alright, just a bit tired," he answered stretching himself. That wasn't a complete lie, he truly was a bit tired, but it wasn't totally genuine either - just like everything.
Namjoon knew he loved him - but thought it was brotherly love.
Namjoon knew he was orphaned - but didn't know anything of his life.
Namjoon knew that he loved the band - but didn't know that he deeply needed all of them.
Namjoon knew a lot but nothing at all!