It's not a typo. It's true that the minimum input voltage documented in the PMIC datasheet is 2.8V, but this input voltage is not enough for powering the whole CC6UL SOM. The minimum input voltage allowed for ensuring the proper functionality of the module is 3.7V, as it was tested. That's the reason why we recommend the range 3.7-4.5V when VIN is used as the input.
When VPWR is used as the input (i.e. front LDO used) we establish the input voltage range 4.5-5.5V. In fact, you can power the module in this configuration with a voltage as low as 3.7V (as the PMIC datasheet say). However, in that case, it doesn't make a lot of sense to go with this front LDO configuration, since you can power directly VIN and the power performance will be more efficient without the external regulator.