Unless the tail rotor stopped working, it'll be pilot error. My brother flew CH53's in the Marines dropping off troops and equipment in the first Saudi war and saw a few helo crashes. It was always pilot error. The old truth saying still stands, "No matter what is happening, Fly The Plane" (or helo in this case).
When I got my private pilots license I was lucky to get all my flight time with a gorgeous 27 year old blonde who had almost every license there was including jet. There were many time during the first few weeks of flying where trying to soak everything into my head I forgot the basic rule, "Fly the plane". The private airstrip I trained from had a runway that only allowed 1000 yards for the climb before you were in the local airport airspace with big jets. Twice I climbed out and forgot to switch over to their frequency and state my intentions. They radioed me of course and asked and of course I felt like an idiot. I knew two of the ATC's there so next time I requested a touch and go there they cleared me to land but just a half mile out they called and switched runways on me....I think to teach me a lesson.
Another time I was coming in for what seemed like a perfect landing after turning to base and just as I turned for final approach I flew threw a wind shear and the plane dropped about 15 feet in about 3 seconds. I had only about 20 hours of flight time then and hadn't experienced this before so I just sort of froze so my instructor immediatly screamed, "I got it" and took over and landed it perfectly as always. She got mad at me after we landed and very sturnly said, "Remember, fly the f***in plane".
As stated, if the tail rotor was fine, it'll be pilot error not flying the aircraft no matter what is happening outside.