Its GL is a little higher. Don't know if higher enough to make that much difference, but my guess it's either because the banana still has its fiber intact, or the possibility you have an allergic reaction to apples.
Is your current diet high in fat? Might need to transition to mostly vegetables at first until the fat in your blood diminishes before incorporating more fruits. It's what I unknowingly did after my week-long juice fast coming off a low-carb/high-fat diet.