And what specifically the rules of the forum violates the possession of one ethereum address by several people?
It doesn't violate any forum's rules but I'm sure it would violate the rules and regulations of the campaign you participated in. There is no campaign that allows participating in the bounties with the alt accounts. I can bet you on that. Participating in Bounty Campaigns is hardly work, unless you are translating something. You got caught, it happens.
Regardless, the point is, clicking buttons 10 times a day from one account isn't a lot of work. Imagine doing the same with the 10 accounts, now that becomes a lot of work. 
So he's correct!