What is the board thickness for nrf52832_qfaa reference design?

I am working on matching an antenna to the nrf52832 QFN package. I am looking at the reference design, which has a 30 mil wide trace. I believe that is supposed to be 50 ohms. However, when I look at the design files in Altium (nrf52832_qfaa), it says that the board is 63 mil thick FR4 with a dielectric constant of 4.8. But, a 30 mil wide trace on 63 mil FR4 with a dielectric constant of 4.8 yields an impedance of about 92 ohms. To get 50 ohms with a 30 mil line width, you need a board thickness of about 17.5 mils.

What is the actual board thickness for the reference design?