I went to a wedding and chatted with someone for 5 minutes and the next day they were a suggested friend on Facebook. Never seen that person before in my life.
I believe Facebook recommendations are somewhat bidirectional - if they visited your Facebook page (by searching you, even if they didn't add you), I think Facebook will recommend that you add them.
This one is easy - Facebook recommends people based on geolocation. It's very common to get friend suggestions to people you've met, or just been in the same building with.
Oh I know. That's creepy to me.
Now the problem is how Facebook got your geolocation data.
I've got a million of these, but one of the weirdest ones was when a friend of mine suggested we go to one of the islands northwest of Seattle for the weekend. The next day, I was googling "things to do in..." and it autocompleted to the island's name, even though it's a relative backwater compared to some of the other places around. Best I can figure is he googled it, they saw us in proximity to each other, then predicted that we were planning to go there.
Geolocation data from the phones could have been used to show you both were in about the same place at about the same time.
Was the wedding a Facebook event that you RSVPed for?
I don't even know how to RSVP for a Facebook event.