Not at all. It is a question of how large they project the 3x3 matrix on the display, and the fact that you don't have a mouse button so moving your finger off the display means you have entered your input.

The geeks who designed the pattern login functionality do support that you twirl your finger any way you like while picking up new points in your pattern. All they do is to display a little arrow in already processed dots, showing the outgoing direction that the line is continuing.

Having this pattern as a security function, you obviously do not want people to find a simple way to connect all the dots with few lines. You want people to find strange and uncommon ways people connect m dots out of the 9. So the phone do not care if you draw your line a second time over a dot. It just cares about if your new line will pass over a previsouly unselected dot.