She stalked off, unhappy that I didn't believe she went to Oxford University. Another spectacularly crashed pick up attempt. Though I'm sure you'd love to hear all about that story, it's not really why I'm here. She believed that I chose to disbelieve she studied at Oxford and as she put it, "...and that's not Oxford Brookes, honey".
Is belief within the domain of choice? I find an extreme thought experiment can be helpful when confronted with a problem like this. Here's one I made earlier:
Try to believe the sky is red. Not imagine it. Actually believe it by force of will. To the point where the next time you look you're shocked that it isn't.
An accumulation of information. My experiences, what I know and what I think I know. That's what decides what I will believe on a given matter. As I continue to interact with the world that act has the power to alter or reinforce my beliefs. From my lofty armchair,a seat on the night bus in this instance (top deck, mind you), I came to the conclusion that her reaction was irrational. Dunno what I was expecting anyway. I mean, it's not like she studied at Oxford or anything.