Basically, he obscures interesting chord progressions of songs he finds by recording his own simplified version without the song's original rhythm. Then he takes his spreadsheet he made over years, of lyrical phrases he came up with that he thinks will sound good in a song, organized by number of syllables and where the accent lands. Then, finally, some time in the futuer, once he has forgotten the original song's construction, he takes out the chord progression and finds places to fit different kinds of lyrical phrases.
It blew us away to know that his lyrics have no meaning whatsoever. In fact, that particular song was the result of a conversation between two teachers he overheard at one of his children's end of year gettogether.
It is quite extraordinary, and he is quite good at it, though we have few Weezer songs in our playlist.