A random misconception about Minecraft I had was that silverfish had a rare chance to drop iron.
The reason I had this misconception is because I didn't know silverfish where real at the time, and I assumed they where made of silver, and the closest thing to silver in Minecraft is iron, so I assumed they could drop it. I was also new to Minecraft at the time. (This was in 2013 and I started playing in 2012)