First that you drove without a radiator cover and if situation like this arises then you should either park the car and let it cooled down for two hours then refill the water or you should let the engine run and pour the water while it?s still running.
Massive blunder, my dear as you poured the cold water while engine was hot and off so it definitely will be blown head gas kit, a repair work which should least cost you around 10k.
Blown head gas kit is a situation once radiator water starts to mix with engine oil. First symptom is what you already told and second will appear within days if you keep on driving that will be yellowish cream underneath oil cover so don?t wait for second symptom to become prominent as that will also damage the engine which can be an additional repair work of around 30-50k easily.