Welder qualification for ASME Section IX and API 1104 have different requirements and do not overlap. Further, you cannot use an ASME WPS to qualify welders to API 1104, and vice versa.
Functionally, from a welding perspective, there will be little difference, but from a compliance perspective, welders need to be qualified to the code of construction using welding procedures qualified to that same code of construction.
He would not be qualified under API 1104. He may well be qualified to weld pipe under ASME B31.4 or B31.8, which permit ASME IX qualified procedures and welders with inspection requirements to API 1104. There are exceptions where welders must be qualified per ASME 1104.
Weldstan is correct. We encourage our facilty fabricators to utilize ASME sect 9 procedures for our facilties that fall under B31.4. We have to review fewer procedures and the welders have to take fewer qualification test because of the way the 1104 groupings are.