Just a thought.
Following on what @TW8punk mentioned, if the case is not weatherproof and the IP rating concerns only fairbuds (the fixit teardown showed clearly some glue in the fairbuds) , would it be possible that the case got wet in your pocket and fairbuds got damaged not because of the rain but because of the case?
Like charging might have been impacted then…
I hope you get your fairbuds and the case(!) repaired for free but it could also lead to some more precise usage guidance.