Updated thoughts.
My primary speculation is that it was a specific someone no one would be surprised by. I think this person was involved with meth, thought that Dylan might have some money, and went to rob him. I think it’s plausible he ran Dylan down with the truck which is why it was cleaned, the front badge is missing, it was in the wrong gear, and the seat moved forward (maybe to get something out from behind the seat). If the truck was going fast enough, Dylan could have been knocked out of his boots. The perp could have then tossed his boots aside.
Runner up speculation: Person A hates person B; they’re absolute enemies. Person A has at least a working relationship with Dylan, perhaps closer. Dylan finds a shoeless person B and gives him a ride. Dylan later meets up with person A, perhaps asking for help moving the grain truck. Along the way, he mentions he helped person B, and person A, who has a volatile temper, becomes angry and kills him. The boots are taken off and left to mock person B (or he also hit Dylan with the truck, again, perhaps fast enough to knock him out of his boots).