Normally the word "whistleblower" means someone who revealed previously-unknown facts about an organization. In this case he's a former employee who had an interview where he criticized OpenAI, but the facts that he was in possession of were not only widely known at the time but were the subject of an ongoing lawsuit that had launched months prior.
As much as I want to give this a charitable reading, the only explanation I can think of for using the word whistleblower here is to imply that there's something shady about the death.
As much as I want to give this a charitable reading, the only explanation I can think of for using the word whistleblower here is to imply that there's something shady about the death.