Perhaps someone who has a better grasp of the standard can correct me, but as far as I can tell, your interpretation is correct and the given example is not undefined behavior.

From 6.5.2.1 (Array Subscripting) of the C11 draft:

"A postfix expression followed by an expression in square brackets [] is a subscripted designation of an element of an array object. The definition of the subscript operator [] is that E1[E2] is identical to (*((E1)+(E2))). Because of the conversion rules that apply to the binary + operator, if E1 is an array object (equivalently, a pointer to the initial element of an array object) and E2 is an integer, E1[E2] designates the E2-th element of E1 (counting from zero)."

From 6.5.6 (Additive Operators):

"When an expression that has integer type is added to or subtracted from a pointer, the result has the type of the pointer operand. If the pointer operand points to an element of an array object, and the array is large enough, the result points to an element offset from the original element such that the difference of the subscripts of the resulting and original array elements equals the integer expression. [...] If both the pointer operand and the result point to elements of the same array object, or one past the last element of the array object, the evaluation shall not produce an overflow; otherwise, the behavior is undefined."

To me, those sections together read that there should be no overflow as long as i is smaller than the length of `points` + 1, and thus no undefined behavior. Does anyone have another interpretation?