You are, of course, correct, but this reminds me of something that I used to deal with on a fairly steady basis when I worked in a gas station, back in the late '60s.
My station was on the NJ Turnpike, and we used to get customers from...all over the US. We prided ourselves on excellent service, and every car got a full fluid check, as well as a windshield washing. Upon request, we would also check and correct tire pressure and clean the rear window. (And...no...I rarely received a tip for the extra services...)
Anyway, when somebody from the Deep South pulled into the station, I could usually anticipate what I would find when I lifted the hood. For some reason, it was very commonplace to find the radiator cap opened one notch, so that it couldn't build up the required pressure in the cooling system. When I would point this out to those customers, the usual response was, "Man, don't you know that it builds-up a lot of pressure if you tighten it all the way?"
The first few times that I encountered this, I tried explaining how pressurization would raise the boiling point of the water in the cooling system in order to curtail overheating, but after seeing that my explanation was...unwanted...I ceased my educational efforts, and just got used to seeing the "southern cars" trailing a plume of steam from their radiator caps.
Of course, these folks also wanted me to refill their radiator, and my standard reply was..."Okay...pull over there for about 20 minutes, and then we can try opening that cap". They always drove away, rather than wait...