EDIT: The claim that Pica is a known disorder is distinct from claims about what causes it. The only evidence given in the post is one personal experience. However, the wikipedia article does state that

scant research that has been done on the causes of pica suggests that the disorder is caused by mineral deficiency in many cases, typically iron deficiency

referencing a study which states that:

Pica is probably a behavior pattern driven by multiple factors. Some recent evidence supports including pica with the obsessive-compulsive spectrum of disorders. Many different treatment regimens have been described, with variable responses. It is important to be aware of this common, but commonly missed, condition.