SES lamp will normally leave a code stored in the engine module which can be pulled up after the fact. Same thing with general check control messages.. they are stored in history. Since they said they "swapped cylinders" im wondering if you had a misfire fault but it was not currently present so maybe they swapped coils, plugs and or injectors to another cylinder to see if when the fault returns it moves to whichever cylinder they swapped it to. Do you have any other symptoms besides the light? Misfiring, shaking, hard start etc. Also make sure with that car that you always run 91 octane or higher "top tier" fuel.