This was a term used by the British music weekly NME in the 1970s and it meant exciting new news and was used ironically rather than as hip slang. As poop is an American word I wondered if they’d got it from Rolling Stone, Creem, Village Voice, etc. or if it was once used by someone like Walter Winchell.
Googling reveals it is a Frank Zappa song with no relevance to the NME sense that I can see.
However, the free online dictionary has
poop 3 (pp)
Inside information: She gave me all the poop on the company party.
[Origin unknown .]
But why poop? I’ve read sentences like “He had all the shit on Nixon” so maybe it is an euphemism.