That Leta and Corvus survived the ship sinking.
Right after Yusuf Kama mentions getting news he’d never expected, he says he’d heard that the ship Leta and Corvus Jr. were on sank, but both Leta and Corvus Jr. survived its sinking.
His servant, Irma Dugard, was a half-elf. Her magic was weak and therefore left no trace I could follow. I had only just discovered how you had escaped when I received news I never expected . . . The ship had gone down at sea . . . But you survived, didn’t you?
Somehow, someone had pulled you from the water!
- Fantastic Beasts: The Crimes of Grindelwald (The Original Screenplay)
Presumably, that the ship Leta and Corvus Jr. were on sank but they (particularly Corvus Jr.) were pulled from the water and survived is the news Yusuf Kama was referring to. He continues on to quote a prophecy, and his interpretation that Credence is the “winged raven returned from the water”.
(to CREDENCE) Somehow, someone had pulled you from the water!
“A son cruelly banished
Despair of the daughter
Return, great avenger
With wings from the water.”
(points at LETA)
stands the despairing daughter. You are the winged raven returned from the sea, but I—I am the avenger of my family’s ruin.
The news Yusuf Kama says he never expected is that Leta and Corvus Jr. were on a ship that sank but survived, which he believed meant that particular prophecy was about his situation.