There are several variants on the NFC protocol. Some contain secure elements (with a CVV3, which is a cryptographically-signed incrementing number), but I believe they can also just dumbly-send the normal card data over the air.
I've also seen credit cards made from glass. I think they're NFC-only, though, because of the thickness, but I could be mistaken.
You are correct in that the NFC is just a protocol but for it to be used without a signature you need a secure element. In their "mock-up" they show a smart car interface on the front and in the FAQ they claim EMV. It is very puzzling.
I've also seen credit cards made from glass. I think they're NFC-only, though, because of the thickness, but I could be mistaken.