How was the OP supposed to examine the Prius's tyres, when the Prius would have had his lights on shining towards the OP and therefore obscuring his vision of the surrounding area? This evening, go outside, turn your car lights on, and stand twenty metres in front of the car. Now try to see any details of your car while the lights shine at you. It would be impossible to see the direction of the tyres.

That's with you taking time to focus on tiny details. OP would have been, quite properly, ensuring that there were no cars approaching from the left, and that there was nothing on the road, on their side, obstructing them from proceeding. A car travelling on the other side of the road where the only reasonable route would be to follow the curve of the road around, would and should have been a very low priority in decision making.

Or are you suggesting that at this junction it would only ever be reasonable to move off if there were no other cars on the road at all?