You were on the skytrain - a public place of people in transit. A transient place! Remember that as the context of your meeting with her, for surely she was well aware of it because she was the passive acceptor of your advances.
That means that you MIGHT have had a small window of opportunity to ask for her phone number or any other real information about her for future contact. If you did ask her, she would have seen the request within the light of being in a transient place with a stranger. She then might have decided it wasn't worth the risk and denied your request or given you a false number, or whatever. Your chances of getting her real number would be very slim. Facebook contact is about as threatening as her phone number. Next time, you should just ask for her email - which shows respect for her privacy and her freedom to decide further contact as she chooses.
Why she would engage in a discussion with you "reinitiating" as she did could be any number of reasons. A lot of females feel pressure to not let a guy feel bad, so they might re-initiate discussion to feign interest. On the other hand, she could be interested but it's hard to tell until you call their bluff - and that's when you should have taken that small opportunity to get her contact info.
A lot of times females want you to express interest in them and continue to do so steadily. You failed to ask for more contact so that might have disappointed her. When you tried through facebook, she might have thought you were just another one of those guys who didn't know what he wants.... so why bother hooking up with another guy like any other. This is quite typical of female pathology.
On the other hand, it could all have been a ruse like I discussed earlier.
If I were you, I would have been forthright and called her bluff at the end of the discussion, but done so by requesting an email contact - then emailed her the next day and not the same day.