I think most likely they were either copper members as well junior members or there was/is a bug.
By the way, can you look at
this?If we have people getting paid without clickable signatures, we are going to keep getting lots of spam.
Copper members can not join bounties before ranking up to Junior members, right?
I guess they often has not get the same payment rates as of Junior rank by simply spending small amount of bitcoin to buy Copper Member rank.
Many people can join bounties even at Newbie and Junior level, and all that takes is 30 activity which can be achieved in as little as two weeks, but it's the signature campaigns that they'll want and there are some that pay specifically for Copper rank and usually at the same rate as Members as Copper membership gives you the benefits of being a Member (which I'm assuming means their signature size):
Available paid memberships:
Copper - 0.00208333 BTC: Allows you to post images even if you are a newbie, reduces the time-between-actions limit, and provides some of the same benefits as being of natural Member rank.