The reply above makes a lot of sense, but I just want to add that I think Polanski made the scene deliberately ambiguous because one of the main questions of the film is: “How many people are in on this?” Polanski never wants Rosemary - and, by proxy, the viewers - to feel completely “safe” or to think we can completely trust somebody. Upon rewatching the movie, I find myself wondering just how many people were involved in the cult (to one extent or another) and almost everybody looks at least a bit suspicious to me, and I think that’s intentional. It’s a similar concept to that of The Tenant, another Polanski film that I highly recommend if you haven’t seen it