premise: "We're an American Band" (from the album of the same name) became Grand Funk Railroad's first #1 single on September 29, 1973, Mark Farner's 25th birthday. Written by Don Brewer and produced by Todd Rundgren, its huge chart success broadened Grand Funk's appeal. It was sung by Brewer rather than Farner, who usually took lead vocals.
hypothesis: The song made the band much more popular
reason: Context provides it was their 1st hit single and "its huge chart success broadened Grand Funk's appeal". My statement says that the song made the band much more popular, which should be viewed as correct. The AI got it wrong, maybe because I used the word popular.