Evans was a Hollywood gossip reporter unaccustomed to having his stories closely scrutinized. If you listen to the interview where he was forced to contradict his own words, you get the sense that he suddenly realized he had stepped into it, and was just trying to back away from a claim he couldn't prove, without admitting he made it up.
If you want to believe someone made him change his story, be my guest. It would be the birther fallback position of expanding the conspiracy to explain away unwelcome news.
So you’re contention is that Evans made up a conversation with his good friend Abercrombie, which never happened, and went on show after show to repeat his lie. He lied about the existence of a BC—or rather the nonexistence—of THE BC of THE sitting president of the US. The next day, wishing to look like a blithering idiot, he retracted his lies, and that was that. No repercussions for lying about the president; no fallout for lying about his conversation with his good friend Neil.
Sorry, that is the most absurd theory I’ve heard since the 9-11 truthers. It is irrational on every level.