Basements aren't "alleged" to stay 50 degrees all year round. It varies almost directly with latitude - in NY, it's pretty much always about 48-52 once you get a couple feet underground. By contrast, in Texas it's pretty much always about 62-65. And that's not alleged, that's reality
A lot of people use this fact to heat and/or cool their homes. Run a few water pipes underground and you can have an effective way to add or remove a significant quantity of heat from the home for essentially free.
It's a good idea to seek shelter if you're going to be in the elements for a while. But you also want to maximize your visibility since people will probably be looking for you. And you need to find a source of water and possibly food. So you can't just head for a cave or basement and hole out there until you die.
And, oh yeah, you can't just survive 50 degrees indefinitely. A guy in a T-shirt and jeans in 50 degree weather for an extended period of time
will get hypothermic, especially if he or she lays down to sleep on the 50-degree ground or a 50-degree rock, which acts as a humongous infinite heatsink.
This is just common sense, of course. An 8-hour "survival" class would teach a bunch of high schoolers pretty much nothing whatsoever that would ever be very useful to them or even stick with them.
An 8-hour BLS, CPR, first aid, or WFA course would be much, much more practical and useful.