Apple is not lying. The IP standards are determined by the IEC (https://www.iec.ch/homepage) and independent product testing labs perform the tests for companies like Apple in conformity with the IEC standards.
But in real world use all water resistance confers is an indication that an IP rated device is less likely to be damaged by water exposure than a non- IP rated device. It is not a statement of waterproofing, nor is it a guarantee that damage may not occur from water exposure.
This is why no company warranties water damage for their IP rated devices other than a few companies offering much more ruggedized devices, e.g. like some CatPhone ruggedized devices. CatPhone has devices that conform to not merely IP rating standards, but MIL-Spec standards, which are even more stringent.