Got a chest, pop up said key fragment

I was so confused I didn't think to get a screenshot or anything. But I knew I had a chest available and I loaded up as Braum support for the first time and got an S+ and I felt pretty good about it since I didn't die the whole game more than once if at all. But at the post game lobby I got a popup for a key fragment which threw me off since I literally got one the game before. It didn't say I earned a chest but I looked at my profile and available chests was deducted by one and it shows a chest earned with Braum.