It's not difficult to come up with scenarios in which the operator cannot reasonably held responsible for an accident. You could be flying miles from anyone else and have a hardware-failure-driven flyaway, resulting in the drone flying into a congested area and causing damage and injury. At the other end of the spectrum, you could be flying over that same congested area to begin with, crash into an obstacle, and achieve the same result. So presenting the question as you did serves as a good reminder not to jump to conclusions, but also cherry picks an explanation that may not be very likely or credible in this case.
We don't, as far as I can see, have confirmation of the circumstances of this crash but, if it wasn't the distant flyaway scenario (has one of those ever actually been documented to have happened?), and since there was an event that might well be the reason for flying in the vicinity, then it was likely pilot error in flying into the tree. Flying into a tree on the side of a road on which a public road race is taking place is poor piloting at best and, given the proximity of the tree to the riders, is not going to pass the "fly responsibly" and "don't fly over people" requirements.
But you are still correct in your underlying point that the cause of the Phantom crash is not yet known. Presumably you are now accepting that the Phantom took out the cyclist though.