Mastery banner on champions bar????

First time poster on the boards, but I've been playing for a while...

So I just noticed this in a bots game with the new 5.22 update.

This guy and I were playing MF and Graves and both had these little icons over our characters on the health/mana bar that resembled the mastery emotes. A few funny things about it. First off I havn't mastered MF yet, and second it changed (both for the better and worse in rank) depending how I did in the game, and third, only us two had them (is it something for only the reworked ADCs?)

Mind you that this was also in BOTS, which you don't get mastery points for. I am so confused, I thought I read the patch notes pretty carefully, but Im not sure I saw anything like this. Has anybody else experienced it, or can give me some info?

Thanks.