The most likely method the artist, Georges Lallemant, used to create the drawing "Reclining Old Man" would be:
by investigating various poses of the human body
Artists often study various poses and the human anatomy to understand how to depict the figure accurately in different positions. This knowledge allows them to create more realistic and dynamic drawings. It is less likely that an artist would achieve a successful drawing of a reclining old man without any study of figures or consideration of textures and value changes, as these elements are crucial for giving the drawing depth and realism.