The most likely scenario I see, is that the left trailer wheel was to the left of the rumble strip, but could still be in the shoulder.
And maybe the car was squeezed by other traffic.
Yesterday I rode 119 miles on my heavy tour bike. I was bothering nobody, 5 feet from the line with a 4 vehicle bunch going by. Long travel trailer, car, pickup truck and another car.
I heard something on the rumbles behind me. The truck buzzed by within a foot of me, seemed on purpose to me. I was too tired to react at all, and going slow into the wind.