I suspect this has to use the Apple Pay infrastructure right? Like transit cards, student IDs, etc. It doesn't seem that NFC Host Card Emulation is coming to the iPhone anytime soon.
I would imagine Apple have been controlling room access like this via an internal app and either NFC or the U1 chip for a while.
It’s their hardware and software, they could easily use internal only API’s and I’m sure there isn’t anyone working at Apple Park without an iPhone in their pocket.