You don't think the fact that Momma went out to buy a box of wine might have a bearing on the case? They might not know if she drank it, or when she might have drank it. But they do know that she bought a box of wine just hours before her baby went missing.
Myself, I consider it pertinent. And I would guess that is really what bothers the parents, more so than the "unidentified man" which could be easily cleared up. Or could easily be cleared up if the parents were talking.
I sure would hate it if something were to happen to me on the 1-2 times a year I might by liquor of any sort - that I hardly drink any of myself. We sure haven't seen anybody come out and say she drank to any excess. Trust me if they could find anything like this we would have heard about it by now.