Most baggage trolleys DO have brakes, which are applied by tilting the towbar hook up, and it locks in place. Sometimes they do tend to go U/S though.........
Most rampies should use the 'six foot rule', which means that anything approaching within 6ft of the a/c should be marshalled by a banksman or manhandled into position.
It is likely that the baggage trolley was being pulled in close to the hold, and someone misjudged the turn radius or the momentum of the cart.
More speed, less haste needed.