That's simply a matter of the definition!

The break point is the (minimum) value of

such that

__no__ set of

points can be shattered. To put it another way, it is the (minimum) value of

such that

__every__ set of

points fails to be shattered. Finding one set of

points that fails to be shattered is

__consistent__ with the existence of a break point, but you need to demonstrate

__all__ other sets of

points have the same property.