Maybe this is just arguing semantics, but I don't agree with the definition you've given, and I don't think that your definition is what TFA means. "Exploiting undefined behavior" I think refers narrowly to the implementation assuming that undefined behavior does not occur, and acting on that assumption. Undefined behavior naturally resulting in unpredictable behavior is not exploitation in the same sense. For example,

  printf("A");
  bool x;
  if ( x ) {printf("B");} else {printf("C");}
  printf("\n");

If at -O0 "AB" is printed and at -O2 "AC" is printed (due to the vagaries of whatever was left on the stack), then that would meet your definition, but I would not regard that as "exploiting undefined behavior", merely as the manifestation of the inherent unpredictability of UB. If the compiler didn't print anything (i.e. the whole block was removed due to UB detection) then that _would_ be a case of exploiting undefined behavior.