TLDR: Cruise had, what some would consider, to be a disengagement incident but didn't report it because it does not fall into the categories defined by California.
The core issue here is that the disengagement reports should not be the end-all-be-all of where companies are. As the ieee article calls out, we have no clue what kind of testing the companies are doing (how hard they are pushing their systems). There is also some room for companies to avoid reporting certain types of incidents.
Waymo did 2 million miles in 2017, but only 330k were in CA. We are only seeing a slice of their data.
If we (the public) want a better picture of where companies are on this, the rules around what is reported need to be changed. They possibly need to also be done at the federal level so no company can hide their public testing in states that don't require reporting.