How else do you define a group led by royalists and other rich western expats, backed by the IMF and armed and supported by NATO, taking over the country and installing themselves as a puppet government in service to western interests? Is a South American coup not a US assassination just because the CIA only supplied the training, money, coordination, and intel and someone else pulled the trigger?
Gaddafi was hardly a beacon of good government, but debt-slavery to the IMF and open doors to the ransacking of national resources by western corporations is hardly an improvement. Not to mention little things like the incidents of ethnic cleansing.