Friday nights in the Mission: a great time and place to have a few drinks, feel good and hook up (if you're lucky), which is exactly what I think I observed happening in this situation. This woman was with a guy who didn't have his bike (shame on him!) and they were trying to go home together so they quickly hailed a cab and she proceeded to fold her bike into a little compartment to stick in the trunk.
I hope they had some good snogging in the back of the cab, although catching a kiss at every stop sign on the way home, in my humble opinion, is far more romantic.
So is riding double (though I might not attempt that on a folding bike). ;-)