Greenspan Concedes That the Fed Failed to Gauge the Bubble

"In his most detailed examination of the causes of the financial crisis, Alan Greenspan, the former Federal Reserve chairman, acknowledges that the Fed failed to grasp the magnitude of the housing bubble but argued that its policy of low interest rates from 2002 to 2005 did not cause the bubble."

Was the housing bubble the disease or just a symptom of a much bigger disease?  You know, like maybe a massive worldwide credit bubble?