Answer:
A description of a piece's structural frame is a statement of plain fact, whereas an explanation of how an artist created a work can also include the viewer's interpretations of the artist's goals motivations.
Step-by-step explanation:
Description is fact without judgement or conclusion. In describing the structural form of a work -- focusing on how the elements of art are composed according to the principles of design -- one states exactly what they see, nothing more.
Explaining the creation of a piece certainly includes such descriptions, but also leaves room for interpretation. In explaining an artist's process and decisions, one is able to ponder why the artist made a particular choice and what the effects of that choice are on both the work and on the audience.