Almost certainly there are multiple problems here. I can imagine a scenario where debris or running over a curb damaged the undercarriage in a way that would a

Almost certainly there are multiple problems here. I can imagine a scenario where debris or running over a curb damaged the undercarriage in a way that would allow water to enter the battery compartment if the lower part of the car was submerged (say, going over a somewhat deep puddle in the road). There are enough Teslas out there that if 'rain' damaged the battery, we'd see tens of thousands of these issues constantly happening. I'm not saying Tesla isn't at fault, or there isn't a design issue, but it's probably some edge case.