Ok guys, thank you all for your answers. Here's how it happened: The flight was completely full, not even one seat in polaris was empty. When boarding, I took the aisle and the door to the toilet wasn't in front of me, its a few steps behind me, next to the galley. There is even some empty space for lining up left and due to that I noticed that people dont line up next to passengers. Many of them dont even know there is a toilet existing at the end of the plane, most of them would go to the toilets in the middle section, causing for a high-time of 9 passengers lining up lol
However, my seat was also assinged for a young lady, our boarding passes showed the same seat. And now, what you some of you have written, happened. An aisle seat in the middle section got empty, I think because of the silvers and the staff put me in that seat.
Now I def. know that I prefer aisles, too. Mutliple times I stood up and a middle seat would be a horror scenario.
Thanks again!