The World Gov assassinated Cobra and tried to kidnap Vivi under Im and the Gorosei’s orders, Sabo stopped them and escaped with her, so they got the papers to report that Sabo was the assassin and that he’s kidnapped Vivi.
☝️☝️Something like that.
Pehaps he give himself to save Vivi and now is captured by the WG. The WG reported that Vivi is missing or was kidnapped by the Revos, while that Sabo have died.
But the truth is that Sabo is going to be used as a bait for Luffy, and Vivi have runned away to try to find the SH and rejoin them, while the WG gonna use this vaccum of power to take over Alabasta, and Pluton, that was theirs real objective in trying to kill the Nefertari family.
Seems to me that the news that the WG wanted to cover was this one about Alabasta and the Nefertari, and the thing Teach talk about in the chapter is the Pluton in Alabasta that he will try to take for himself.
Could even bem that Kuma used his powers to send Vivi to the SH or something like that.