I'd say just move on and find another bounty. The threat of negative feedback was probably an empty one anyway, and most bounty managers, to my knowledge, don't make false accusations so as to deny payment and/or blacklist members. Either way, I'd be interested to hear his side of the story.
The Admins and project's team doesn't want to reveal the auditor's BTT account because the auditor wanted it to be private. These "Auditors" are a group of active and trusted members here in the forum as they have claimed. I'm waiting for the ANN thread for the result of their investigation. If they don't present any credible and solid proof for their accusations then would you lend me a hand to clear up my reputation?