alt Hacker NewsThis is anecdotal evidence but Dennis Rodman (the pro basketball player) was the greatest rebounder of all time. One of his teammates related to how he would watch guys shoot (usually during warmups) and count the rotation of the ball. Based on how many times the ball would rotate, he knew if it was going in or not and then would position himself to get the rebound.
I would imagine OP did something similar. Watch the coin as its rotating and then grabbing it and then flipping to the side he predicted.
Sandy Miller is widely considered to be the best volleyball player of all time. He would famously wear the same unwashed shorts every game for good luck. Maybe this was his trick.