How is getting a log book different from tech inspection?

A log book is simply the official record of the car’s competition history. Since the logbook just covered the initial build of cage with seats and harnesses, there are a number of other critical systems that need to be checked at the events to ensure that the vehicle is ready to compete.

For example, you'll probably get a log book after your cage and seats are installed. Things like your fire suit, helmet, fire extinguishers, the expiration date on your belts, these would all be checked at the event during the tech inspection process. They would not need to be in place for the initial "get a log book" process.