A misconception here is that he was not actually driving a full rig, but the tractor only.
His most like story at the gate would be that he was there to pick up a now-empty trailer that hadn’t been fully unloaded before he finally left to go into town for food, fuel & required rest period. No bill of lading needed coming in, because no trailer, let alone load.
Not intended to excuse or mitigate anything about the security; just a correction of what he was driving.
Thank you for taking the time to clarify that point.