Well, it was only a matter of time before someone's iPhone 4 overheated. Believe it or not, it wasn't left in in a car in a mall parking lot on a 105 degree day in sunny Austin, TX, either. Where was this iPhone?
It was in the user's pocket, in their car with the air conditioning turned on. Perhaps this person releases a lot of body heat, or maybe their AC doesn't work as well as we assume it does. In all seriousness though, it's strange that their iPhone 4 would have this kind of problem given the conditions. As least we know that the warning looks more beautiful than ever on that gorgeous Retina display.