I have tagged him as well. It seems to be his habit as uncovered by YOSHIE, and hopefully It will be a lesson learned for him. I think I have also had my Bitcointalk account username being used for bounties and airdrops by such cheats not so long ago.
The people who apply for bounties using other member's details can even put one's good account into danger of getting banned or tagged as people might think they are alts. I am very shocked that some bounty managers just pay participants minus even confirming if the person owns the social media accounts or not.
Good thing that this was already tagged, if I may advice, OP should also report this problem because this is a serious thing. It is identity theft after all, there might come a time that not only bounty cheating will be their only use of this kind of trickery, a lot can happen trust me and I guess I would speak for everyone that being accused of something that you don't even have the knowledge or the guts to do so is such bad feeling, having someone getting away from a crime and you becoming a safety net for them is the worst thing that can happen to anyone. I suggest that you guys that got your social media copied by bounty cheaters to report it to local authorities, tagging them as bad guys in this forum is not enough.