Cheater just copies your username and profile link and registers for the bounty.
Cheater can do this with as many accounts as they want well aware that reputable members like you could never visit the bounty section to participate in the bounties
This mostly happens with bounties who managers do not emphasize proof of authentication
I have encounter that so many times I have at least three entries scammers using his own wallet, that is why only participate in a bounty campaign, where there is a proof of authentication, or visit the spreadsheet more often to check if there is double entry of your name.