It isn’t that the song is a cover, it is not credited to the author.
And while Page in the citation steers the discussion to riffs, the lyrics and title are the basis of the suit.
The drum beat from the intro to Little Richard’s “Keep a knockin” was used to lead into “Rock and Roll”. But that’s just a section of something (and Keep a knockin” wasn’t even Richard’s song, it’d been recorded by Louis Jordan in the 1940s and dated all the way back to the 1920s).
I just always assumed that all those old blues numbers they “electrified” were older than dirt and in the public domain.
Claiming credit for writing them is quite different.