Hey, I just won the battle buddy achievement! However I have only done two battles against buddies.:p I played my second one a few minutes before and then I started the weekly challenges. When I finished the second challenge suddenly a pop up appeared saying I completed the battle buddy achievement!

I'm not complaining or anything :p but it looks like a bug :)

confirming, I got it after just 1 game, actually, we played remach and I got it at the start of that second game :)