When they refer to rendering. It isnt like rendering in 3d. They dont use some rendering tool to make it. When they say rendering they mean how the drawing was done..
found this online, pretty much explains it as related to drawing/painting
A rendering is simply an interpretation of a figure/object/scene. A drawing may be termed “a good rendering” or “a bad rendering” depending on how closely or how well the item being depicted is drawn. The term “rendering” may also refer to a perspective drawing that is created of a future structure.