Yes the announcement shows if you ever pressed the advance button that is the league you will be in next season for chest rewards.
For example, if a player reached Diamond league at any point in the previous season (meaning they achieved both the required rating and collection power and chose to advance to that league) then in the current season they will earn Diamond loot chests no matter what league they are currently playing in.
https://peakd.com/splinterlands/@splinterlands/splinterlands-ranked-rewards-update
I find it best to be the top of the league than in the bottom of the next one up. I average 9 silver chest per day in the daily focus at Silver 1.
So they changed it back. That is interesting. I guess next season I will just need to be careful and not click the button like I did this season.