They never actually used the stolen tech, right? It wasn't good enough. They hit the pedestrian solely on their own tech, which (clearly, in hindsight) wasn't good enough either.
The pedestrian ultimately got hit because a lot of fallback systems failed: They disabled the software's ability to emergency-break (1), they disabled the cars' systems to emergency break, and the operator of the vehicle was distracted, not reacting in time.
(1) This was actually done due to false-positives, i.e. the car slamming on the breaks in non-emergency cases. (I find that's a relevant point, because without that detail it just sounds more ludicrous than it already is).
And the emergency breaking relied on the human operator but the system was not designed to warn the operator.