I suspect that @RickJay 's point isn’t that the Beatles weren’t “rock music,” it’s that they weren’t technically “rock and roll” – which, technically, is true of the vast majority of the artists in the Rock & Roll Hall of Fame.
From a narrow, technical definition of “rock and roll,” it was a popular music genre which peaked in the 1950s, and largely died out by the time of the Beatles, having evolved into (or replaced by) rock music, rhythm & blues, etc. as the predominant forms of popular music in the U.S.
That said, a lot of music fans still use “rock” and “rock & roll” interchangeably.