is it really sexual harassment? He tried clumsily to make a move on her and she declined, if he tries again it's a red flag, but if he stop his behavior you have nothing to worry about
Referring to a colleague as a 'milf' is not 'clumsily making a move'. Everyone knows what that's an acronym for. If you start a private chat with a colleague, they tell you to keep it about work, and then you tell them you'd like to fuck them, then you should expect to be fired.
absolutely is. It's not a clumsy making a move. That would be "hey, do you want to go have dinner some time?" Calling someone a milf is not something ANYONE with any respect for women would ever do.