Bishop73

Answer: Spock understood how the machine worked, by sending a person to the time they were viewing. When the three were near the time portal, they could hear each other and those around them. Spock would have been able to hear the group of people who took Kirk and heard them talk about thievery, purse cutting, and the law, etc. He made a logical assumption Kirk is in a more advanced and "civilized" time period that would have to be much later than the ice age.

Bishop73

Answer: He was seriously injured during a rescue mission, the result of the accident and his injuries also left his mind unstable and he began a descent into madness. While not a lot of detail is given, you can compare it to war veterans who experience shell shock or PTSD.

Bishop73