Minecraft Achievements Come Up while not actually earning them

I was playing Minecraft and i got an achievement while just doing casual work in the game. This happened twice:

I was in a friends world when i got the into fire achievement. I haven't even seen a nether fortress in survival mode. 

Also I was playing creative in a no achievements world when my freind fought the ender dragon. I set his game mode to survival, and he had no glass bottles and still obtained the "You need a mint"