Transmigrate to Ancient Greece and Conquer It

I didn't understand it at the beginning of the book. Why did Pig's Feet self-destruct as a time traveler after traveling to a city-state to prove his identity? He started fighting with nobles in a confused way. It didn't explain what role Pig's Feet played. The part about finding things in the library was even more outrageous. The knowledge he obtained from the system was forgotten in a blink of an eye.