I don’t think the “erratic behavior” quote is related to the stock Volvo emergency braking system. The report notes that that also existed and was disabled (justifiably) while Uber’s self-driving system was active. But apparently Uber’s own system had an emergency braking function that was also disabled:

> At 1.3 seconds before impact, the self-driving system determined that an emergency braking maneuver was needed to mitigate a collision[..]

[emphasis mine]

> In Uber’s self-driving system, an emergency brake maneuver refers to a deceleration greater than 6.5 meters per second squared (m/s2).