I think it's possible the poor driver was not using TACC before the collision, and therefore "AutoPilot" was not involved.
But first, let me be clear that, to date, "AutoPilot" or "AP" has specifically meant TACC -- plus or minus AutoSteer. Not Enhanced AutoPilot (EAP), although TACC is (or was) part of that package. It never did and does not mean standard cruise control. It's easy to see why the non-Tesla world is utterly confused by these naming conventions. Tesla didn't help with the recent refinements to its price lists. Going forward, TACC and AutoSteer will be packaged as such, and everything else now in EAP or FSD (including software and hardware) will be sold as AutoPilot. Oy.
With that cleared up, here's why I think the collision could have been a non-TACC, non-AP event, assuming the trailer was detected at all:
-In a non-EAP M3 (without TACC), with or without standard cruise control engaged, travelling at 55MPH, EAB would deploy to reduce the impact speed by 25MPH, then release the brakes. At that point the car still "underrides" the trailer at 30MPH, faster at higher speeds, with no further pedal inputs. This seems fast enough to do real harm given the awful physics involved, while leaving enough momentum for the car to roll some.
-In an EAP M3, with TACC were engaged at 55 MPH, EAB would have been applied to full stop force upon detection, and I believe it's likely the car would have come to a complete stop sooner if fully braked at collision than if braked-and-released. So the longer roll distance suggests no hard sustained braking applied. I'm just speculating and could be 100% wrong. A finding that TACC actually was engaged would make this a legit AP fail scenario. But it would have to be an EAP M3 WITH TACC engaged to check that box.
I do feel a connection to this crash because it's so close to home; could have been me on a road I travel often; could still be someone I know; the facts make it a matter of unusual human interest, and not in a good way; and people need to know that some crashes cannot be avoided even with the best available technology.
Regrettably, the trailer could have been practically invisible to sensors and humans in this particular situation.
I'm going to watch how local media and officials cover this. We'll all see the national coverage.