One can have multiple accounts, even more than 100 accounts, the forum have no such rules to have only one account. But there are some community standard which are like
You can not join same signature with multiple account
You can not send merit to your alt accounts
You can not join with multi account from a signature and many more.
Have any of the account done such offense? If they did then we can tell they were cheating, otherwise all good.
[Sorry, my tor is too slow to load images]
Could it be a group who worked together?
I agree with you on this one and I really don't see any rule or policy restricting people from having multiple accounts but as long as they aren't doing anything wrong, then I see no reason in calling them cheats and in the other hand, I don't think growing of account is actually an easy task because it takes so much time and dedication to grow an account and growing several accounts wouldn't be an easy one.
I think those accounts might be some group of persons working together and it seems they are participate in bounty campaigns and I'm sure you can't enrol one social media account for two different bounty groups.
You did a nice work @OP and it's not easy doing a voluntary work especially as a newbie just to get tye forum clean.