well you did have something happen which the ECU decided was serious.
there are 3 different levels of faults you are going to get.
1. low level - fault code will be logged but the engine management light won't be illuminated. you may notice minor behavioural changes in car, such as slightly stuttering when cold (as an example but nothing serious and may not even be noticable.
2. medium level - fault code will be logged and the engine management light will be illuminated. limp mode will NOT be activated. light will stay on for the next 6 engine start/stops and if no longer present light will go out. fault code remains logged. sensor has detected something more serious but it does not directly affect engine or vital component integrity.
3. high level - fault code logged and engine management light illuminated. limp mode activated. this means something has been detected that poses a risk to the engine should it be allowed to continue, so safe mode has been activated. this warrents immediate investigation.
a firm favourite with turbos is overboost, you have have unwittingly triggered an overboost situation without realising, which will throw a turbo car into limp mode as you won't be allowed any boost pressure.
without checking the fault codes you will never know of course. what you do need to remember is that this is something the ECU believes it has detected, so its a sensor reporting a value outside of normal range. this doesnt always mean something has gone wrong though. it could be that the sensor is failing and so sent an abnormal signal to ECU or that you have wiring damage between that particular sensor and the ECU which could fool the ECU into thinking there is a problem when there isn't.
thats why you need to investigate the fault code first, then we can start naming and shaming particular components / sensors etc that could be at fault!