The pdf says
"The castellation connection for the antenna on the pre-certified version allows the use of embedded antennas as well as removes the cost of a cable assembly for the U.FL connector. However, the PCB design and layer stack must follow one of the reference designs for the certification on the HUM-900-PRC-CAS to be valid. Figure 91 "
This is for the castellation version only not for the UFL
It also clarifies and says
"Note: The PCB design and layer stack for the HUM-900-PRC-CAS must follow these reference designs for the pre-certification to be valid.
The HUM-900-PRC-UFL and the HUM-900-PRC-CAS must use one of the antennas in Figure 108 in order for the certification to be valid.
The HUM-900-PRC has not been tested and requires full compliance testing in the end product as it will go to market.
All modules require unintentional radiator compliance testing in the end product as it will go to market."
Again the pcb layer stack reference is for the CAS version only! the UFL just has to use one of the listed antennas in Fig 108 for the certification to be valid.
At least this is how I understand what is being stated I have not heard back from the supplier to confirm and I will be out of town for the next week I hope that I will hear from them by then.
Thanks