I know there is a really low probability but this can happen, am I right ?
Just like the serial numbers on a call card, it is impossible to get corresponding numbers.
With a small difference:
Amount of possible private keys: 2
256 -> thats 1,15792089 × 10
77Amout of possible numbers (with 20 digits for example): 1 x 10
20So there would be about 10
57 times more private keys than possible numbers in your example.
Thats way way worse (in terms of relation between those two) than comparing the flip of a coin to winning the lottery.