Leaving aside that Lecter is a famous psychiatrist and would have had experience of such a common psychiatric disorder, the fact is that Lecter knows who Buffalo Bill is.
This is not really covered well in the movie for, I suspect, time reasons but, in the novel, it is made clear that Lecter had a patient, Benjamin Raspail, who was ...
I see those as Marianne vision of insecurities about losing Héloïse . The dress and facial expression of Héloïse is fragment of thought involving Héloïse getting unhappily married and looking at her at despair. She feels somehow responsible for that for avoiding her.