Immense loss friend! Sorry to hear that.
Could be several possibilities. For people who just rely on what they can only see normally. The car circuitry is always live and even a single minor short circuit can lead to this, reasons may be multiple. Only after surveying the car, we can get an idea what it could be i.e. arson, accidental, manufacturing fault, electrical circuitry, or unprofessional after market installation.
To emphasize, yes we can not neglect manufacturing fault just because it is Honda, at this stage we cannot comment it is for all BRVs but for this particular car. This is where quality control comes in, after all same people did blunders with their flagship i.e. Civic.
Regarding electrical circuitry, one thing that comes in my mind, is rodents, considering where the car is parked. They do eat away electrical wires and associates. The other thing is improper electrical installation by Honda (Not blaming them but people who work at Honda are Humans at the end of the day).