Whoever said this has no clue about experimental probability. If you roll a six sided die for 6 times it is likely that you will not get number 6 within those rolls, however if you roll it 100 times, there is a good chance you will get a 6 (almost certainly). The shiny encounter rate is just like a massive die with 1/8192. Although each several roll is independent, on a bigger scale your chances of getting a shiny is increasing.