I think it wrapped things up, that it was all in his head, but real in the same time. Bob Cody referred it to Neal while they were in the car: https://clip.cafe/interstate-60-episodes-of-the-road-2002/ever-hear-of-frederick-turner/

Some people say we have the frontier of the mind, and they go off and explore the wonderful world of alcohol and drugs, but that's no frontier. It's just another way for us to fool ourselves.