Can a faulty coil pack be misdiagnosed as a head gasket?

I broke down on the motorway when my car began to lose power. I couldn't accelerate and when I pulled off and slowed down the car was chugging and almost bouncing. At the scene the recovery driver diagnosed it as a head gasket problem because there was water in the oil and a orangey gunge. His garage then quoted me for the repair to which I said I couldn't afford. They then phone me later saying that it's not the head hasket at all, it's a faulty coil pack.
Does this sound plausible? I'm a bit suspicious.

The Engine managment light was on prior to this happening if that has anything to do with it.