Oddly peculiar arena rating achievement bug[?]

[dnawlols]

So I've noticed over the past little while that some of my older alts are randomly getting 1550/1750/2k achieves (toons that have not been levelled since tbc/wotlk, however some have been still played on). I was trying to see what was proccing the achieves but alas I cannot find a concrete answer. Sometimes I get the achieves when logging in, sometimes I get the achieves on my first arena win, sometimes I get it after losing a random arena. I haven't been able to see what exactly is causing this but I'd like to ask, has this been happening to anyone else?
https://i.imgur.com/qVT1cfm.jpg
https://i.imgur.com/WbmRpRg.jpg
https://i.imgur.com/GaqN0LK.jpg

I had another SS with my ret getting 1750 in 2/3/5s after losing my first arena on it (still did not have step into the arena ach). I also have done arenas on my warrior back in cata in the 70 bracket, which is also why this is odd (just a few games, did not play enough to even get 1550). My priest even, was level 60 until cata when I got her to 85 and didn't touch her whatsoever.