89 Nissan Sentra 2 DOOR, 200,000

My car is presently in the shop.
Here is my experience and question
I was driving when I heard hissing from my car, suddenly there was steam and my car died. You can see steam coming from the area of the water pump. Next morning we put water thinking it's the water pump. Shortly thereafter it leaked from the water pump. The car was not turn on. Thinking we need a water pump we went to the mechanic. The mechanic stated the water pump area still leaked, so he said that the head gasket was blown. Is this possible and if so, how?
Thank you for any response