One of the pieces of information you are not providing is the condition related to backing.
The filler metal being 6010 does not mean it was an open root joint.
If a joint was welded without backing during the performance qualification test, then the welder would be qualified with or without backing.
If backing was used, then the welder would only be qualified for cjp groove welds with backing.
Backing is not just a backing strip or ring. It could also be weld metal in double welded joints.
Have a good day!