I haven't seen much evidence that the stars move in concentric circles.
For the star trails to be perfect circles the lens can't have any significant distortion and must be perfectly aligned with one of the two pole stars, and that star must be in the center of the sensor.
For a lot of artistic shots this is not the case, and you will see visible distortion. This is not unusual, you see distortion in plenty of photographs. Taking pictures of the sky is no exception.
And as pointed out, you didn't draw your circles centered, so of course they are not going to line up.
This is a picture I took myself, with the camera centered on the North Star and using a lens with very little distortion. It's not perfect, I had it set on the roof of a house and the slow cooling during the night warped the trails slightly but as you can see, they are quite circular. I'd show some of my better ones, but for the same reason Jay gave, I do not want to give up my location here.
I've taken lots of pictures like this and can assure you they do move in circles.