Why Does My iPhone Think a Nexus 7 is an Apple Pay Terminal?

I had rested my iPhone 6 on my Nexus 7 today and something weird happened: Passbook opened up on my phone and asked me to use my thumbprint to authorize a payment. “huh?” I asked, understandably confused. Here’s video showing it off:

I don’t know enough about NFC and Apple Pay to know how this happens. I presume it has something to do with Apple Pay looking for a certain frequency, but I’m not sure. If anyone has a good explanation, I’d love to know!