It's making an advance for the eventual goal of sex. How is that not a sexual advance? How is an email chain between interviewee and interviewer, discussing your interview results, not a professional setting?
People go to GREAT lengths for the "eventual goal of sex" all the time without it being labeled a sexual advance, including striking up what may seem like friendly conversation even though you may never have the slightest idea that their end game was actually to screw you (among many other things). Arguably the majority of anything that people do is for the eventual goal of sex.
The e-mail "later that evening" was not discussing the interview results. It was a later email, presumably on his own.