What about LUCK?!

Yesterday I was super lucky, I gained 2xShiny Chest from 8 Low Bounties, more than nothing, as i guessed. The first one droped 100, so round number, the second one droped 1 (ONE) !!! Shiny Crystal, that time I LOLed, what is the chance to get 1 from a Shiny Chest? while it says: 1~500, so means 1/500 or so, and i was that lucky to get 1 (ONE) !!!