Yes you're right it is static and static only. When refuelling aircraft you have to earth the aircraft and bowser this doesn't stop the static inside the tanks. Boeing used to show a film inside a fuel tank as it was being filled, it was like a firework display.
However you are more likely to...
Ford introduced this system so there's no need for a cap. Normally in the glove box though may have been moved is what looks like a slender funnel. This is designed to release the flap if using a petrol can to fill up with. If you can find it try pushing that in, giving it a shove if need be.