The Universal Life Church is an organization that provides ordination for anyone who wishes to become a minister, regardless of their background or beliefs. While it is a legitimate organization, it does not offer traditional academic degrees.
Thompson, who was known for his unconventional and rebellious nature, likely saw humor in the idea of being ordained by a church that doesn't require traditional qualifications. He used the title "Reverend" ironically, often as a way to subvert the expectations of a conventional religious figure.