It could be safer than human drivers and still cause quite a few deaths. We can't evaluate such statistics from one accident. We don't even know if this particular accident would have been avoided by a typical human driver (there was apparently one behind the wheel of the vehicle).
That's reasonable while the system is in testing and in small scale use. If it ever becomes a major part of the transportation system, it won't be desirable to shut it all down every time there's an accident.
