To compare two items or individuals usually means to show ways in which the two things are similar and how they are different.
Professor Herbert is well-educated in terms of formalized learning coming from schools and experiences in the academic world; Luther Sexton has extensive practical knowledge of the natural world but no formal background education and, at first, very little patience for those who place much importance on "bug larnin'."
The professor's appearance and speech patterns reflect a culture and personal lifestyle that is very different from Luther's way of life and attitudes. The Professor "wore a grey suit of clothes" while Luther "wore overalls, big boots, a blue shirt, and a sheepskin coat and a slouched black hat gone to seed at the top."
By the end of the story, however, both characters have shown their flexibility and willingness to learn from outside experiences. Professor Herbert will approach students coming from the "hills" differently as a result of his encounter with Luster, and Luster has gained an appreciation for the changed type of learning that Dave is receiving.