Passenger window down

this is about my 2018 Enclave Avenir.
We got back from a cruise and as we approached the car I started using my key fob to unlock. It was dead. No response. I had parked the car in backwards with the back 1/3 stocking out from the covered parking. When I got to the car the passenger window was down and the car had water everywhere all over the inside. There was 2" of water on the floors. All the doors were locked. I gained entry on the passenger door bc the window was down. After getting some of the water out I tried to start the car but everything was dead. A cop showed up and as soon as the jumping cables were attached the alarm belated and I started the car. My question is this... What would've caused the window too just spontaneously open. My assumption on the water is there was a huge storm with horizontal rain that happened after the window opened on it's own? I hate coincidences.