Was it parked pointing downhill by any chance? Water sometimes enters via the hinges for the rear hatch and runs forward on top of the headlining.
I saw somewhere (i think in a youtube video (?)) where the owner got some draft excluder tape and made a sort of 'dam' along the top of the hatch opening (effectively underneath the 'spoiler') so that any water entering between the roof and the hatch was diverted down either side of the hatch with no chance of running down where the hinges or grommets are.
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