What just happened?

-15 minutes ago-

I am riding on the train back to my apartment and I am standing near the door listening to my ipod. Across from me, sitting down, is a younger good looking girl who has a smile on her face and earphones in. I naturally think she must be listening to something funny (Flight of the Conchords maybe?). I am tempted to ask but don't.
To the right of me, sitting a couple seats down is a younger guy with curly hair, tight black pants with a cuff, pretty clean and average looking. He has a rather stern look on his face which I noticed only briefly.
Occasionally while reading my book, I will look up and keep noticing the girl with a smile on her face, looking down into her lap. My stop comes, and stern faced indie guy stands next to me to get off, and flannel coat smiling girl also prepares to get off.
Stern Face walks quicker than me even though his stride is shorter (I walk casually and am in no rush) and goes up an early flight of steps. I am surprised to find Smiling Girl walking at a rather quick pace as well, passing me as we get to the turnstall. Smiling Girl is right in front of me walking up the steps, and while I am still interested in what she was smiling about, I have no intention of asking.

Outside. I see Stern Face walking a good half block ahead, and Smiling Girl a couple paces in front of me. She has a good pace going now, as do I. Before I know it, we are close to Stern Face and I see her reach her hand out and touch his shoulder. He jumps slightly out of surprise and has a confused look on his face. Then I see Smiling Girl put her index finger to her lips in a "shh" motion, and start to lean in towards his face! I pass them both right at this second and don't want to turn back and watch whatever just unfolded before my eyes. Did she really just approach a complete stranger and kiss him without a word?
I don't slow down but turn to cross the street, and glance back to see them following. I hear some laughs, possible talk about where each of them live on the block, and possibly an invite over? I paused my ipod at this moment because I wanted to be sure, but didn't hear anything else and didn't see either one of them at the next block.

But what happened just now could've been the hottest thing I have seen in a while. I think it trumps my missed connection story.