After I removed all the clothes, and saw more black crayon stains, this is what my dryer looked like:
Here is the culprit:
I googled (is that a verb now?) "how to clean crayon out of the dryer" and the answers said to take a damp cloth, spray WD-40 on the cloth, and wipe the inside of the dryer. It worked to get the crayon that was caked on, but most of the stains will not come out. I think the dryer was so warm that it permanently melted black crayon into the drum. Every time I look at the dryer, I will remember to always check Thomas' pockets!
A picture of my sweet boy, who only was warned never to put crayons in his pockets again!