More precisely, according to what the gorilla knew, Eobard Thawne's fate was missing in action.
During the "Rebirth" event, Reverse-Flash attacked Doctor Manhattan because of Barry, then vanished without a trace. After that, everyone lost ten years, and no one could clearly remember what had happened during those ten years.
Deathstroke had mentioned while chatting with the gorilla that Manhattan had rebooted the Multiverse, merging the Watchmen Parallel World into the current Earth-0. But afterward, Doctor Manhattan died.
No one had any clue how he died or who did it.
Later, Deathstroke had even seen Manhattan again. Quantum Mechanics seemed to have thrown time into chaos.
Those were beside the point. The reason Bobo believed Reverse-Flash was dead was simple—if Reverse-Flash were still alive, could he really hold himself back from coming to "play" with Barry for more than half a year?
Just like how Joker could never hold himself back from playing with Batman for half a year.
Reverse-Flash was Mr. Barry Allen's most fanatical admirer. Sure, his obsession had driven him insane and twisted his humanity, but he was still a fan.
Dr. Swann believed he and Barry shared an inseparable bond. For a time, he had even believed that he was Barry.
He had once helped The Flash grow stronger, allowing Barry to run faster. Yet at the same time, he was also the murderer of Barry's mother.
More than half a year had passed since the "Dark Metal" event after "Rebirth." Everyone had been busy during that time, but Barry had remained active at Deathstroke's side. Wherever there was a fight, Barry was usually there.
If Swann were still alive and had seen such a lively Barry, he should have shown up long ago to demand a race.
That was Bobo's reasoning, as well as a