An explosive atmosphere could exist in the cabin of a vehicle if the hand sanitizer were in a wide, open container with a large surface area resulting in a high rate of evaporation. Since hand sanitizer is typically packaged in enclosed containers with only a small vent to allow air to displace the volume of fluid dispensed, the container will not continuously vent alcohol vapors unless it reaches its boiling point of ~175°F. Therefore, the only area with an explosive atmosphere would be inside the container which would have to reach ~700°F before it would ignite.But, the temperature in the car would have to be above the flash point temperature, not the boiling point temperature, to have sufficient alcohol concentration in the air to create a flammable mixture. For isopropyl alcohol that's around 55 F.
Now, if you brought an open flame right up to the little vent hole and squeezed the bottle a bit, you might ignite the mixture inside the evaporated alcohol inside the container. The rapid pressure increase would cause the container to rupture and likely propel burning sanitizer all over. That's when hings would get really bad.
Point being is that you'd have to try really hard to get a bottle of hand sanitizer to explode and I don't even see how it's possible without bring an open flame right up to the dispenser. I suppose a black vehicle parked out in the open sun on a sunny, 120°F day might get hot enough to cause the alcohol to boil out of the container, but even if it did, there might not be enough vapors from an 8-ounce bottle of 70% alcohol to exceed the LEL resulting in an explosive atmosphere. (I might get bored and calculate that later.)