Hextech Chests

So, I've read that in order to get these chests, it's either through mastery, or if any of your premades get any kind of S rank in game, and through that you will receive a chest. It is written here: http://na.leagueoflegends.com/en/site/2016-season-update/champion-mastery.html "When you or someone in your premade party earns any S rank, you’ll acquire a chest." It doesn't say you "might", it says you'll acquire.

Yet in my last game, one of my friends got an S rank on Jax, yet I didn't get a chest. This isn't the first time either, Countless times there as been an S rank and there has been no chest. I think i've only gotten one chest ever since this whole crafting thing has started.

So is it bugged for me somehow, or is this just misinformation? :S

PS: I have no idea on what subtopic this would go, hence it's in gameplay.