This sounds quite a bit like massaging statistics until you get the numbers you like. A few things that pop to mind: did we exclude drivers who were not eligible to drive (under the influence, no valid driving permit, cars with issues [braking broken]...)? (This mostly matters for evaluating the average performance compared to average non-impaired human — a drunk person might mess up with self-driving vehicle sensors…
If our current system of checks and incentives is not able to keep them off the road, then you need to take them and the accidents they cause into account when comparing driving safety with an autonomous system.
Also note that the margins are too big, since only about a third of accidents involve intoxicated drivers, and the accident reduction rates from the paper are much higher than that.
I don't want to come across as harsh or accusing, but the "Methodology" section contains a lot of detail (and a more nuanced discussion could be had without disregarding it entirely :P).