And let me pre-empt the replies by saying yes, what matters in safety is the statistics, not a single data point. And let me pre-empt the replies to the reples by saying yes, but the statistics on self-driving cars are not at all encouraging.
I suspect Autopilot's running-into-semis rate is worse than humans', for three reasons:
(1) Tesla has been cagey about their Autopilot safety stats. If Autopilot was clearly safer, I think they'd be less cagey. Absence of evidence is evidence of absence. This is just speculation, of course.
What concrete data they have shared is summarized here: https://www.tesla.com/VehicleSafetyReport
Teslas with Autopilot on crash roughly once every 3 million miles. To their credit, that's really good! However, they don't say: (1) how often Teslas crash on freeways with Autopilot off, or (2) how often drivers have to take control to prevent Autopilot from crashing.
(2) The fatal crash in 2016 was also with a semi trailer. 2/4+ fatal crashes having this failure mode suggests this failure mode is especially high for their vision based system. Not a good look.
(3) Pretty much all self-driving companies have disengagement rates way worse than humans. Waymo is leading the pack - by far - at something like once every 10,000 miles in California. There are tons of caveats in interpreting these numbers, and they should probably be treated as an upper bound, since it's at the discretion of the company to only self-report disengagements that would have led to crashes, I believe. But human crash rates are something like once every 300,000 miles. So even lidar based systems are an order magnitude away from humans, by one super rough measure.
Lastly, a small correction to the title: This is the third known US autopilot crash. I believe there was a suspected autopilot crash in China some years back as well, and I'm not sure about other countries.