He's always absent-minded and answers you as though he's unconcerned.
He's not always there when you talk to him. When you ask him a question, he answers as though it is not his affair at all.
この場合、次のような言い方ができます。
ーHe's always absent-minded and answers you as though he's unconcerned.
「彼はいつも上の空で、他人事のように答える」
absent-minded「上の空の・ぼんやりした」
unconcerned「関係がない・無関心な」
ーHe's not always there when you talk to him. When you ask him a question, he answers as though it is not his affair at all.
「彼は話しかけてもいつも上の空で、質問をすると他人事のように答える」
not always/all there「上の空で]
one's affair「人のこと」
ご参考まで！
カナダ 
