Well, I say tell him to look at the O2 sensor. I know when my car wouldn't start, bmw said it was my sensor. It went bad out of no where. Other then that I doubt it's the ECU but it could happen.
O2 Sensor info. is ignored [or not read] until car goes in to closed loop mode.
In other words, until the car warms up, O2 sensor has nothing to do with starting the car.
Please correct me if I am wrong.