Interviewer: Ricky Gervais [of "The Office"] told me there's a story that Liam thinks Spinal Tap are a real band. Is that true?
Noel Gallagher [of Oasis]: Yeah, he thought they were real people. We went to see them play in Carnegie Hall. Before they played, they came on as three folk singers from the film A Mighty Wind. We were laughing and he said: "This is shit." We said: "No, those three are in Spinal Tap. You do know they are American actors?" "They're not even a real band?" "They're not even English! One of them is married to Jamie Lee Curtis." "I'm not fuckin' 'avin that," he says, and walks off right up the middle of Carnegie Hall. He's never watched Spinal Tap since. He'd seen the film and loved it and thought they were a real band.
[Here's the story in London's Guardian. Thanks, Stereogum!]