Yes, reading their posts, especially several posts in one session shows google you have found what you wanted, and that site must be a quality one. It does help their rankings whether you enter through search engines or not.

I'd say that visiting a site through google and staying on there for one second, then leaving without clicking on anything at all tells google you didn't find what you are looking for. It would add to their bounce rate. But it would take sooo many of these type visits. Who has time for that.