I'm sure it seemed like a good idea to him at the time. Really not enough information to tell what exactly went wrong other than the dangers of doing something alone that should have a minimum of two.
Reading the brief article, it would appear there were two people at least. Assuming the reporter got confused (as they usually do) between "jump-start" & "pull-start". I don't see how a tractor could tip over while jump-starting a car and pull-starting would require a second body in the car. Maybe the person in the car didn't know what they were doing and rammed the JD when the engine caught? Lot of possible scenarios for this one. Sad, whatever the cause.