instead, he was absorbed in computers and spent almost all his time in the computer lab of the university.at last,he and a friend of his started their own software company.

위문장에서 his는 어색한 쓰임 아닌가요...? him을 써야 할꺼 같은데... 교과서 지문이니, 틀릴리는 없고... his를 써도 되는 이유가 궁금합니다.