It's rather UX bug, but everytime I look at reports, AVERAGE PLAYER ELO section always has green arrow pointing up, no matter if I got plus or minus stats for last day. It's not major issue but my OCD told me to report this :D
From my knowledge, the arrow indicates the change of your rank for that stat, maybe a few teams dropped further than your team so you placed higher overall than previously. Eg.. Your team on 2200 ave elo, mine is on 2203, we are ranked 1 & 2 hypothetically, once the daily updates go through, my ave elo goes down to 2190 and yours drops to 2195. Your team is now higher than mine and your rank increased accordingly.
Yes, it indicates change. When you got minus stats, then you got red arrow pointing down, if you've increased your stat, there is green arrow pointing up. I made a screenshot to show how it looks like http://imgur.com/a/6bPDa and it'w always green arrow in avg player elo section.
That would make no sense Wilo because you're almost higher than someone, its 100% a bug
It makes sense to me anyway, its hard to explain. because i have had many times when a stat has decreased but i had green arrow cause my rank in the stat increased