Hi Sakuragi86
I will like to ask you a question, will you say "hi" to a guy who
have say "hi" to you? I believe you will right? That is the most
basic manner. Will you talk to him if he talk to you? I believe you
will too. After chatting for a while, you have to alight, will you
say bye to him? I believe you will. But does that all mean you
interested in him?
Maybe not.
I frankly feel it is nice to chat with a stranger in a bus
especially thing like "have a nice day", "a wonderful day" and etc.
But dont you feel that you shallnt jump into a conclusion so fast
as the person maybe interested in you?
I guess I dont have to answer why she dont give you the number. If
a guy you just meet ask you for a phone number in the bus, will you
give? 
Regards