Was the ignition key left on while any sensors were disconnected during the spark plug change? If say you had disconnected the air flow meter or throttle position switch while changing the spark plugs and turned the ignition key on even briefly to operate the windows or turn on the radio the computer in your car would have seen an open circuit in the sensor and brought on the light. Many sensors are shared between the engine, transmission, traction control ect.... If there is no "true" fault the computer will look for a fault and in a few days turn off the light once the correct criteria is met to run a "drive cycle test". If the light stays on something has become disconnected, damaged or just coincidence that the traction control system now has a fault.