First of all the style is locs. "Dreads" is a term you people gave them based on how dreadful they looked to you...ie your reactions to the style. They aren't awful, dirty, or disgusting...it's how African hair grows when its not chemicalized. Wow!
To answer your question, yes locs are curls. People of African heritage are the curliest. Locs are formed by not combing the hair and allowing the curls to collect. What you call a "dread" is simply millions of curls that haven't been combed.