We had snow the other night and I forgot to grab a box of stings I had just purchased out of the truck of my car. Do you think the cold could hurt the strings ?
At temperatures where there still is snowfall, I don't expect either Nylon or metal of strings to be affected unless they were wet to start with. If you dropped them in liquid nitrogen, it might make sense to bring them up to room temperature slowly before doing anything with them, in particular unpacking/unwrapping them, and there might be structural damage.
But a car trunk in regions where you don't have to start your car with a fire under the oil pan seems harmless enough.
Yes steel strings will lose some of their factory temper if exposed to extreme cold or heat. Phosphor bronze will lose some temper if heated up too much such as leaving the guitar in the sun on a hot summer day. They will become a little deader sounding. And after steel strings are played for a certain amount of times the temper will start to leave them. They will get harder to tune. Steel strings are only as good as the temper of the steel or bronze. Coated strings will lose their temper as quickly as non coated but keep looking good because they're coated from the elements. People who post info should make sure what they're saying is fact and not just their opinion.