It makes sense that the trailer backed over the pole so far it got under the bar. But the trail behind the pole indicates that it was dragged forward. It seems like he backed over the pole causing it to bend and go under. Then moved forward causing it to poke out above the rail and then it dragged forward causing the asphalt to be ripped up the way it did.
But why didn’t the bar break? It must be made of alien materials!
And who put the pole in the middle of the parking lot? Probably bigfoot.