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.