Answer:
Tom's eyes started off as a black line, but later transitioned into empty, black sockets. He inherited this peculiar trait from his "mother", a bowling ball. In a second Tumblr post made after the end of Eddsworld: Legacy, Tom offers his intended explanation for his character's black eyes.
Explanation:
The African culture does not typically use a stringed guitar-type instrument
When drawing a continuous line your pen/pencil never leaves the paper
