Complex sentence: For that comic he was the "Big-Background Artist," which odd credit refers to his role in pencilling and inking the larger and more detailed background designs only on select panels and pages, rather than throughout.
Split into simpler sentences: For that comic he was listed in the credits as the "Big-Background Artist". That odd credit refered to his role in both pencilling and inking the larger and more detailed background designs only on select panels and pages, rather than throughout.