As I understand it, the firmware in Kindle is based on unix/linux. The system clock in all unix/linux computers is set to GMT/CUT and the clock display is based on the time zone relative to GMT/CUT. The Kindle may be time stamping files based on the system clock time, not the displayed clock time. If you are on the pacific NW, you are at GMT -8 time zone.
The reason to set the system clock in all unix/linux systems to GMT is to allow easy, accurate comparison of data located in different parts of the world. Small differences in time can make a big difference in some types of financial and legal transactions.