It’s highly unlikely he won’t get his money owed, they cannot simply decide to not pay for work which has been carried out, as I understand it he’s not after the money for two hours he did before taking the truck back.
I can’t believe people would say not to claim, or take them to court, if your current boss didn’t pay you for a days work and you’d left his employ the following week/day there are people on here who wouldn’t take him to court for money owed? Christ 
Luckily I don’t have to work on agency, but there’s no way I’d get treated the way some agency guys do. The people who run agencies are just as bad as estate agents, idiots in cheap suits who think they’re some big shot business men, parasites in my mind.