Love can make you go blind
Not just that, he totally ignored that Emma introduced herself as Bailey.
He didn't even know Josh's first name until he asked the assistant, do you think he knows Josh's last name at all lmao
I think at some point he does, because iirc he knows Josh's full name and the secretaries's full name, when he in a future chapter confronts Josh with it.lol
I don't think that he is the sharpest Miller, because he also has difficulties identifying Josh as an omega. I mean later, when their relationship changed, he got so many clues, but... .
Miller is so ignorant, he didn't even notice how Emma and Josh's eyes and hair color looked similar.