k. Let's do that, then.
https://www.eeoc.gov/laws/types/sexual_harassment.cfm
"It is unlawful to harass a person (an applicant or employee) because of that person’s sex. Harassment can include “sexual harassment” or unwelcome sexual advances, requests for sexual favors, and other verbal or physical harassment of a sexual nature."
or
https://www.eeoc.gov/eeoc/publications/fs-sex.cfm
"Sexual harassment can occur in a variety of circumstances, including but not limited to the following: [...] The harasser's conduct must be unwelcome."
Unwelcome sexual advances. That's your black and white definition. Being called a MILF can be an unwelcome sexual advance.
Being called a milf ----LITERALLY---- means you are a mother I would like to fuck. Regardless of how you perceive pop-culture to use the term.
It ----LITERALLY---- is an acronym for mother I want to fuck. There is not another interpretation. You're wrong. You're just wrong.
As for:
>If this occurred as OP described, I don't see how it can be construed as sexual harassment. He ended contact upon her making it clear that it was unwanted, so by the very definition of "harassment" he didn't harass her.
OP said nothing about how the male employee ending contact. He said that the female employee "handled it well and didn't let it get out of hand." That is something entirely different. That means that, had the female employee not ended the contact herself, this could have gone on.
EITHER WAY. You're just wrong. This could be perceived as harassment by a female employee.
Now, whether or not the guy should be fired really depends on what OP learns when s/he interviews both parties, after s/he talks to a lawyer. Honestly, the EEOC or lawyers or courts would try to determine if the actions were pervasive (I don't think they were) and created a hostile work environment (sooooo grey, maybe this did, maybe it didn't).
I'm telling you that you're just wrong. That's not phrased as a question - it is a declarative statement.