Well Im not sure about this but iirc the odds to actually hit it would be 0.00499%
The chance to get 10,000 in free roll is 0.005%.
Every time you play free roll, a decimal number which is between 0 and 10,000 is calculated and it's rounded off the nearest whole number. For getting number 10,000, that decimal number must between 9999.5 and 10,000.
That actually is almost correct statistically if we assume that the real odds is 0.00499% then that means it would be to hit one every 25,000 rolls
It's expected to hit 10,000 once in every 20,000 rolls on average.