What is the distance metric in dynamic time warping?
The Euclidean distance between two vectors $\mathbf a$ and $\mathbf b$ is $\mathrm d(\mathbf a, \mathbf b) \equiv \sqrt {\sum_i (a_i - b_i)^2}$

In your example you forgot to square the differences. Remember the way you calculate hypotenuse of a triangle; it's the same idea.