Manning originally changed his own story.
I don't believe she ever described the situation as a "mooning". That word was invented by a Tennessee athletic department official.
From the Deadspin story:
"Within hours, Naughright said, she reported the incident to the Sexual Assault Crisis Center in Knoxville. Rollo found out what happened, saw that she seemed truly upset and bothered by what had happened, and asked her not to call the police. He also tried to “fix it,” the facts of the case document says, by helping Manning come up with the story that he actually had been trying to moon teammate Malcolm Saxon and that what had happened was an accident.
At first, Manning denied anything had happened at all, according to the document. During his deposition, Rollo took the responsibility for it being referred to as “mooning.”"