I am no forenisc expert, but logic tells me that either this unfortunate person had not frozen, so was not dropped from a longhaul flight, or he defrosted after landing on the car roof, whch implies he was there a fair while.
It would require many days of subzero temperatures to freeze an entire body. It's not like freezing a cut-up chicken. However, death from hypothermia can occur when the blood temperature is as high as 80 degrees F.
Why do people do this? Because it works. Some have survived. And you are sure to get a hearing in front of whomever are the powers-that-be. That's probably better than living in a sewer/slum at the end of a runway. A well-prepared person - thermal clothing, supplemental oxygen, restraint system, knowledge of the landing gear bays - could easily pull it off.