They seem to be misunderstanding what he said in the interview they cite, because I don't see any mention of the whistleblower dying, just her husband (who died in 2011).

She was the wife of the former owner who died under suspicious circumstances. And, she was willing to give up all of the offshore bank accounts, including the Bidens’ accounts.

This is the line I'm guessing they're using as evidence? Which is clearly talking about the former owner dying under suspicious circumstances.