Parking Accident – 50% partial debt?

Hello, I had an accident at the beginning of January on a Lidl parking lot. It snowed on that day, the place was full of snow and slippery. I drove into the driveway, left and right are then each parking areas (still add the sketch below). Directly in front of me a car set to park, backward in my direction steered. I immediately got on the brake, but because of the weather conditions did not come directly to the stand but slipped about 2m further. The other car did not stop the parking process and drove me into the passenger side while I was still slipping. The accident was taken up by the police. The accident opponent said she had already parked and stood. Both are with the same insurance and they decided now: “The accident opponent indicates that he has already confessed at the time of the accident. However, this cannot be understood after the accident analysis. On parking lots there is the principle of mutual consideration. Since you could not get to the stand, but have slipped further into the vehicle, both accident sufferers are liable to 50%.” For me this decision is not understandable at all. Mutual consideration to or from, more than braking I could not. Apart from the fact that I am nevertheless “flowing traffic”, and that it is at the time of the accident that I was able to If I miss anything, I would do the damage (3.7k€) via the UK, but I don’t really see that as long as no one can explain to me why I get 50% blame. I don’t have an RS.