The unexpectedness of it. If you live in a major city & work in IT, you can expect that a large number of your cow-orkers will be Weird in some way: queer, poly, kinky, trans, Pagan or militantly Atheist, into bikes, etc. So running into workmates at an "alternative" event, or running into people you know from an "alternative" event at work are both relatively common events.
If you're at a private event for members of your institution, it's unusual to run into someone who you know from a different context because you'd have been far more likely to run into them at the institution first. I seriously have no context for running into bi/poly people at uni because I only know one other person who does even vaguely similar work to me.
Anyway, it turns out that she has no personal connection with my institution and it's simply that she knows someone who works there, who invited her because her job is interesting. And we had a nice chat with euphemisms.