The messages the OP refers to could be some sort of scam or spam.
As far as gas on a hot day goes; gas can expand and overflow a completely filled to the top gas can. When you fill up you are bringing up “cold” gas that is stored in a large tank perhaps 10 foot or more underground. The temp of the gas in the tank is in the 50’s. Once in the cars tank the gas can heat up, how much depends on the day and conditions. Hot air and even hotter pavement can heat the gas in the tank up to something close to 100 degrees in Arizona desert heat. A 50 degree increase in temperature will cause the gas in the tank to expand. In modern cars this expansion is captured in the tank and evaporative control system so fumes are not released into the air.
In old cars you could see the results of expansion in gas leaking out the filler pipe and onto the ground. You don’t see that anymore because the expanded gas is handled internally by the car, but damage to the evaporative control systems, primarily a damaged charcoal canister, can result. The result is a check engine light and an expensive repair to get it turned off so you can pass state emission testing