He called her a milf to her face. That's completely unacceptable.

She was clear when she said "as friends at work". It wouldn't have been harassment if he hadn't been so crude and suggestive. if he'd just said "hey, want to have dinner some time?" Then it would have been a little forward, but not harassment. He didn't. He said "You're a mom I'd like to fuck".

It doesn't have to be ongoing to be harassment. Once you've declared "I'm the kind of guy that'll call you a milf to your face after only knowing you a short time"... all bets are off. Any time you're alone with him, you're going to feel uncomfortable. And I guarantee you, that kind of guy is not going to be a perfect angel the rest of the time. He clearly has messed up ideas of what is appropriate to say to women.