Because Tony Stark only met Dr. Strange in infinity war and Thor had met him before if Thor had returned to visit tony inbetween Thor Ragnarok events and Infinity war...
(Cannon.. Whats cannon???)
Tony: So your telling me theres a mAgIcAl pORtal WiZArd who has a magic cape living downtown.. Yeah sure buddy
Thor: It is true Stark he produces portals not even seen on asgard. By Odin he was impressive
Tony: Lemme get this straight this "magical wizard cape man" lives in a massive house downtown that only sometimes certain people can see
Thor: Exactly : )
Tony: Sure......
(When he meets Dr. Strange)
Tony: THOR WAS RIGHT HOW WAS THOR RIGHT?!?!??

















