Depends on the girl and the situation IME, Curve. If they think you're chatting them up and they're not interested they'll just blank you, but if they think you're just having a conversation then they'll chat away. I've definitely been in plenty of situations where a girl has ignored me when I'm just talking. When they were rude I would tell them their shoes are ugly. That would always get some kind of response.
I'm a lot nicer these days.
Conversely lots of girls have been too responsive when I'm chatting them up and have no chance. That was always tough because it felt like wasted time and effort. Nowadays I would look at it as good practice, but at the time there were only so many hours on a night out in which to get busy.
Anyway a guy with a camera producing a doco probably presents enough of a neutral atmosphere that they are comfortable with him. Those guys are practiced at getting people comfortable enough to be open and honest with him based on a few minutes of conversation. I'm sure there's an element of skill to this, but it's easier to do when you genuinely don't want to **** them!
Anyway, this is probably Girls101 to you guys, but always think it's important to make your intentions clear from the start, be they amorous or not. That is easier said than done when you are relying on a stranger to correctly interpret your intentions. I would lean back from somebody if I was just talking to them, and if I was trying my luck I would try to make physical contact as much as possible. Most girls would respond appropriately, some still took things the wrong way and had their footwear mocked mercilessly.