Correlation between credit score and credit card balance

MM posts on PFBlog about his year of 0% arbitrage where he borrows money from credit cards at 0% APR and makes money by putting it in a savings account. He also posts a graph showing the correlation between his credit score and his credit card balance. It's interesting that after the one year of keeping a high balance, his credit score has actually gone up. Here's a screenshot of that chart.