No, it's not. A C&D letter is a legal threat or warning. I could send you a C&D for sneezing too close to me.
Having received a C&D letter myself from CL, I can assure you there are multiple issues they claim. You can find this C&D letter at DocStock. CFAA violations are one claim, copyright violations are another.
(On an aside, doesn't their terms of use disqualify access with a browser, or really any piece of software?)