Even the researcher doesn't claim that Alex contacted the CEO of Synack because of a dispute over the bounty.
Rather, it's the other way around: the researcher disputed the bounty, and did so by revealing that he'd retained AWS credentials from Instagram long after they'd closed the vulnerability that he used to get them.
Alex contacted the CEO of Synack to ensure the credentials weren't used, because if they were, Alex couldn't be control Facebook's response: they've got a bug bounty participant who has essentially "gone rogue" and is exploiting Facebook servers long after they've told him to stop. They need him to stop.
Even the researcher doesn't claim that Alex contacted the CEO of Synack because of a dispute over the bounty.
Rather, it's the other way around: the researcher disputed the bounty, and did so by revealing that he'd retained AWS credentials from Instagram long after they'd closed the vulnerability that he used to get them.
Alex contacted the CEO of Synack to ensure the credentials weren't used, because if they were, Alex couldn't be control Facebook's response: they've got a bug bounty participant who has essentially "gone rogue" and is exploiting Facebook servers long after they've told him to stop. They need him to stop.