Why does the narrator in "The Red Convertible" switch to present tense from past tense?

For my english class we are reading "The Red Convertible" and I have to figure out why the narrator switched from present to past tense in the scene where Lyman is describing the relaxing moment.

Here is the scene...

"I do remember this one place with willows. I remeber I lay under those trees and it was comfortable. so comfortable. The branches bent down all around me like a tent or stable. And quiet, it was quiet, even though there was a; powwow close enough so I could see it going on. The air was not too still, not too windy either. When the dust rises up and hangs in the air around the dancer like that, I feel good. Henry was asleep with his arms thrown wide. Late on, he woke up and we started driving again. We were somewhere in Montana, or maybe on the Blood Reserve-it could have been anywhere. Anyways it was where we met the girl."

Any help is appreciated! Thanks!