Over 80% of aircraft mishaps are attributed to pilot error. Very few are associated with mechanical difficulties as well as other factors (ATC, weather and other things).
So, yes, in about 80% of the time the pilot is responsible but NOT always. How can you can say the pilot is responsible if a mechanic used the wrong bolts and a wing falls off or a flock of small birds suddenly flies up into the engine?
With the stated conditions, it clearly is because he didn't exercise good judgment, and he and his passengers are still dead. Actions he may have taken just prior to the crash make it so they are heroically dead.