Tesla battery packs are sealed. They even have pressure valves to equalize internal and external pressure changes, you can often hear them “pop” when supercharging due to the temperature increase from fast charging. Water doesn’t just get into the battery pack from simple rain.

Either there was a defect in the manufacture of that specific battery pack and it’s seal, or the owners are lying about the circumstances. Both are possible but people lie all the time about what they do with their cars, especially when they know it’s going to be an expensive repair they want to have covered under warranty even though they caused it.

There are numerous videos of Tesla vehicles wading obviously deep water they should never go through and working just fine immediately after, who knows after it sits for a while if that action damages a seal, but simple rain is extremely unlikely to do what they claim.

The article doesn’t give any explanation other than the couple saying it was rain, and Tesla saying the batter had water ingress. No photos, no further explanation or information from the owner about what the vehicle was doing or where it was parked. Rain and subsequent flooding then driving through, partially submerging the vehicle would cause that sort of damage and you could still say it was technically just “rain”.