The Volvo collision system had been disabled, the Uber system didn't detect the woman crossing the road, and the driver was watching Hulu or similar on her phone. Uber had also gone from teams of two doing the autonomous testing to teams of one.

Oh yeah, and Uber released a super contrasty picture to justify their car's behavior. Less biased sources showed that there was plenty of visibility on that stretch of road.

If you're looking for sources, Ars covered everything in pretty good detail.