I was playing in survival mode on a friend's realm (on Minecraft PE/bedrock, iOS), and I got a spontaneous notification that I earned the Into Fire achievement. For context, I have never entered the Nether, nor seen or held a blaze rod in the realm. I was just smelting some items in a furnace and working on an underground base. There is no reason I should have gotten that achievement. Also, no one else was on the realm at the time, if that helps.