* Hug people they've never met.
* Put their hands on people's legs seconds after meeting them.
* Put everything a particular woman says into the frame of "Women don't do X."
* Assume that women who attend tech meetups are exclusively there as the girlfriends of the men present.
I've had it go both ways and end in sex, although never in a professional setting.
This may be a cultural thing, but I wouldn't touch (in an intimate way, like a hug or thigh grope) someone I was interested in without a pretty clear sign it was welcome. It's just not appropriate.
Why should the onus be on the person being touched to stop it, and not the person touching to not do it? What if someone you showed no interest in touched your genitals, for example?
If she wasn't interested, she should have stopped it immediately. - what if she didn't stop it but still wasn't interested? Where does that leave her then?
You have to assume 'this is probably not ok, unless it is communicated to me otherwise', not 'there are no objections, I'm carrying on'.
The only response that she could have made to encourage his behaviour would have been one of enthusiastic consent.
You might have had a positive outcome from this technique, but that doesn't make it right. I can't comment on your experiences but, in general, the fact that an interaction ended in sex does not mean that that interaction was consensual.
It's your responsibility to tell me that I'm not allowed to joyride your car.