(Standard lawyer disclaimers apply here–I am one, but not yours, and this is just talking on the webs, not legal advice.)
If someone kisses my jacket on the bus is that sexual harassment?
So, this isn’t quite an answer to the question you asked, but it’s relevant. My recollection (though it’s been a few years) is that torts like battery don’t distinguish between hitting a person’s body, and hitting something that is attached to or worn by a person. (This, by the way, makes pretty good sense: if somebody swings a baseball bat at your head but you’re wearing a bike helmet, you don’t want them to be able to say “I just hit the helmet.”) And battery itself doesn’t have a minimum-force requirement: it just requires offensive touching. (That said, I’m having a tough time imagining anything other than nominal damages in a case like this one.)
I haven’t had any experience with sexual-harassment law (other than the usual employment-orientation lectures), so I’m not sure whether the same tests apply in the context of sexual harassment specifically. But I’d think they would. Imagine Creepy Male Boss uses a ruler to flip up his female assistant’s skirt. Zero skin-to-skin contact, but I presume you’d agree that we’d want to treat that as sexual harassment, right? And my suspicion (based on exactly zero tenths of an hour of research) is that the law would treat it that way.
(Obviously, Italy’s legal system and laws are completely different than here, though.)
In this specific instance, I agree with the point that the police are overreacting–and that the point of sexual-harassment laws is to protect people who are otherwise powerless. But I don’t think the legal question is as clear-cut as it might seem.