This is a map created in version 0.12 before the achievements were implemented. Mods are installed but not activated. I also played modded multiplayer maps. Maybe some destroyed trees from these multiplayer maps or in 0.12 destroyed trees counted for the right progress bar. (I loaded the 0.12-savegame and the migration overview doesn't mention destroyed trees.)
After reaching the 100/100 trees the achievement triggered in game and steam.
