How does Charley confirm that Sam has traveled to the past?

Charley confirms that Sam has traveled to the past when he receives a letter from Sam that was mailed from Galesburg, 1894. In the letter, Sam describes his life in the past, mentioning the old-fashioned details that confirm he has indeed gone back to the time Charley believes he had visited. Charley is astonished to learn that Sam has successfully found the third level and settled in Galesburg, further solidifying Charley’s belief that the third level is a real, magical gateway to the past. This letter serves as proof that Sam, like Charley, has found a way to escape into a simpler era.

This question related to Chapter 1 English Vistas Class 12th NCERT.
From the Chapter 1. The Third Level.
Give answer according to your understanding.