As much as you want to scream fraud, I think you should have posted the announcement thread link to the bounty as well so we could check that out in detail and see how this is all lined up.
He did but maybe you didn't notice it. tranthidung wasn't responsible for managing the bounty, was only responsible for posting the thread. It's not the first time happening this. A lot of forum user has posted bounty for other people. Project use the reputation.