You can approximate the length of any path (including circles) by adding the lengths of many small line segments that follow that path. Making a line segment bigger by some factor, will increase it's length by the same factor.
Therefore, scaling the circle by any factor, increases it's circumference by the same factor.
Scaling a circle is just scaling it's radius so: Scaling the radius by some factor, changes the circumference by the same factor. That means the ratio between radius and circumference is always constant.
You can approximate the length of any path (including circles) by adding the lengths of many small line segments that follow that path. Making a line segment bigger by some factor, will increase it's length by the same factor. Therefore, scaling the circle by any factor, increases it's circumference by the same factor. Scaling a circle is just scaling it's radius so: Scaling the radius by some factor, changes the circumference by the same factor. That means the ratio between radius and circumference is always constant.
I hope this is decipherable :D