He doesn't know anyone by that exact name. It's her doctor name from that previous conversation she had with her master, not her official name. It might be normal to think "Su huh, might be related to the Su family I've been meeting recently," but either way he wasn't introduced to anyone with that name so they'd have to investigate it either way.
I mean, ML knows that MC only met Meng Huichun recently.
If I heard stuff like "inherited his divine legacy" and "outstanding medical expertise" I would not think that meant someone he taught for a few month(s) using books and a straw doll.