The pins are only upside down based on your frame of reference. If there was no you, no Earth and no gravity, only the apple and the pins the pins would have quite an argument deciding which of them was upside down.
Your feeling of something being upside down is based on your frame of reference where "down" feels like a direction towards the center of the Earth's mass, which is the direction gravity is pulling you. For someone on the other side of the globe, down to them also feels like it would be towards the center of the Earth. Gravity exerts a force which holds everyone against the Earth, no matter where on it they are standing. The idea of a down is purely based on this frame of reference.
If you were looking at the Earth from a great distance, how would you determine what part of the Earth was upside down? Imagine the Earth is flat and flying through space. You are held against the Earth by the force of its acceleration. Your frame of reference of down would be towards the ground because that is the direction you feel the force holding you. If you were observing the disk from the side from a great distance, what would stop you from thinking the Earth was traveling sideways, or even down?
What's up and what's down is all perspective based on your frame of reference.
Don't know if that helps at all.