Circuit breakers trip when too many amps flow through the trip or there is an earth fault on the circuit.
When you first turned on your grill, there was a fault (either a short circuit or earth fault).
Many faults clear themselves when they first occur, (the act of a minor explosion at the root of the fault causes the fault to blow clear) this is probably what happened with your appliance.
Fault causes could be, debris left from the manufacturing process, damp components or strands of cables touching the wrong bits.