Ok one time is an "occurrence." However twice??

If you dont know, i had an earlier thread where my first premium box was a championship thresh http://boards.na.leagueoflegends.com/en/c/miscellaneous/lyB7ZzZJ-omg-i-just-got-championship-thresh-from-the-free-hextech-case

Now i go to my alt account and i open the box on that one again..

What is the % chance of this even happening, let alone getting another championship skin LOL?