"Minor" head gasket leak

[Indy]

Just throwing this out there for some feedback / educate myself about what is going on with my Z.

The situation is that the car lost most, if not all of its coolant last week due to what the dealer diagnosed as a cracked lower radiator hose. Basically I saw smoke out of the left side engine bay and smelt coolant, drove 500 m to find a safe place to park and as soon as I parked, the car let go and emptied a good 3+ liters (approx. 1-1.5 gals) of coolant on the side of the road (I could hear fluid flowing and gurgling, not just dripping).

Car was towed to a holding yard as it was Sunday and then to the dealer, and was driven on its own power a few meters each time to get onto and off the tow truck. This was 3 days before I went overseas, and now after enquiring over the phone at the dealer about the status of my car, they said they found a small "incidental" head gasket leak. It is covered under extended warranty and they had the entire engine out of the car apparently.

My car is entirely stock and an 09 MY. It is my daily driver with 77,000 km (50,000 something miles), no other problems, and I baby the hell of it with occasional spirited bursts given the time and place, however no track days. Any idea what may/likely is going on that has required the headgasket to be replaced?
Appreciate the feedback!

*Oh, I forgot to add, I check fluids and oil fairly regularly (not every fuel stop, but at least once every 2 weeks), and didn't see any signs of coolant mixing with oil or vice versa, basically no signs/symptoms until my car proverbially pissed itself.