driven with 40% petrol instead of diesel and nothing noticed

In our company, 22 liters of normal gasoline were filled yesterday by an employee in the 52 liter tank of an Astra H, 1.7 l CDTI BJ 2008 (no doubt, video recording of the tank is available, as well as the tank receipt), so 30 liters diesel plus 22 liters of normal gasoline, and then the good lady drove 450 km mainly BAB and federal road, without, she says, even the least thing to notice on the vehicle / engine. The thing was only noticeable because the tank card refused the booking (is just on Diesel programmed) and the amount had to be paid in cash today The vehicle was towed today by our company to Opel and is now being examined for damage. So the car was safely driven over 450 km (drive book record). The question is only HOW? We ask ourselves now whether the engine in such a case does not give any signals that it is uncomfortable… ringing, power loss, unround running or dying in idle, wrong display in display o Whichever. Does anyone have any personal experience with such a situation? Can it be that the engine runs easily without sounding, even though it has over 40% gasoline in the tank?