That is probably not the explanation. The ultrasonics can only detect objects out to 16 ft away, and their relatively slow latency means that at highway speeds the AEB cannot come on in time to prevent a collision. It might have been activated, but too late to prevent the crash.
There are a number of reasons why the Tesla driver might have failed to notice the truck in time to prevent a collision. I do not think that the AP being activated is the reason for the crash.
@MorrisonHiker posted upthread, quote: "The FHP said the tractor-trailer was traveling west on US 27A in the left turn lane toward 140th Court. Brown’s car was headed east in the outside lane of U.S. 27A.
When the truck made a left turn onto NE 140th Court in front of the car, the car’s roof struck the underside of the trailer as it passed under the trailer. The car continued to travel east on U.S. 27A until it left the roadway on the south shoulder and struck a fence."
That description makes it sound like the truck driver did not see the oncoming Tesla and turned directly in front of it. We do not know if the Tesla driver attempted to brake or if by the time he saw the truck he did not have time to apply the brakes or if he never saw the truck at all. The car's logs will show if the brakes were applied by the driver or the AEB before impact.
Whatever the reason for the crash, all Tesla AP owners should know that they have to remain alert and aware at all times while using AP. Using AP on a road with cross traffic, even a divided road, has always seemed risky to me.