I run Mobil Synthetic blend (new car formula even though its a 94...whoops ) Is that bad by the way?

But yesterday i was toppin off my oil ( i dont have leaks, i just didnt fill it to the top mark when i changed the oil, and so i was just topppin it off...But when i took the oil cap off to pour it in steam was comin out...i cant think of why it would be steaming, steam comes from water...right? there shouldnt be any water in my oil. I thought it may be coolant leaking into my oil but, i had the coolant flushed not to long ago by the dealer in a 120k service, and they didnt say anytrhing...

Any ideas, is it normal, when your car is hot, go take that cap off and see if yours steams too...