I always thought that IP54 was just fine in rain. We installed lots of outdoor stuff on sites that was IP54 rated I am sure and I cannot remember it being an issue at all and we had some pretty rigorous inspectors checking on stuff before sign off.
As someone mentioned earlier in this thread this has the hallmark of being lawyer-speak that is only there to reduce or remove the liability of the company in the event of something happening whilst the car is being charged in the rain.
IP54 is an outdoor rating for sure and outdoors means being able to work and be used in normal weather so this does mean rain proof. It is no good against something like a hosepipe or pressure washer though as that could blast water upwards and I think that IP54 only gives protection from water that is mostly coming downwards or from the side and not underneath.