Naïve
There's a reason why Neji is called "all-seeing".
It's not just because of his Byakugan. His life has forced him to see everything as it as.
So when he sees Team 10 trudging wearily back into Konoha carrying Asuma's body (they refuse to call it a corpse), he doesn't see Ino shrieking in anger and pain at anybody who dares to touch the body but Shikamaru, Chouji and herself. He doesn't see Shikamaru smoking his sensei's old cigarettes. He doesn't see Chouji rejecting offers of food which are always ready when he comes back from a mission.
He only notices what he can't see. He can't see the three children which left Konoha, anxious to help their sensei. He can't see the three children which used to bicker endlessly.
He can only see three adults.
They know what the real world is like now. A world where people die, where blood is drawn, where angst is inevitable, where sadness is everywhere. He can see through to the pain in their hearts.
And in his own, he mourns for the three children they were.
Because they're still children, maybe, and the world is just forcing them to grow up too fast.