I think all of those feelings are all mixed up anyway. What are "erotic" feelings and how do they differ from the nice feelings of being loved in a parental way? Maybe it's the desire and excitement or maybe it's the difference between, being done to (being loved in a passive way) and wanting to do (wanting to express our excitement and love). Freud would say that we experience sexual excitement from the very beginning - the joy and bliss of being fed, cleaned and touched in a gentle, empathetic way. There's loads around the Oedipus complex too.
When he talks about himself in those terms, I guess he becomes more human and a man with sexual desires (talking about dating and past partners), so maybe that's why your buttons are pushed?
For me it happens when I feel a strong connection in the session. I think I sexualise emotional connection, I find it highly arousing... I think because I'm not really used to experiencing it.