Huge Superflat World Error

A huge chunk island spawned in my superflat world like I copy and pasted between worlds.

I tried to do it again with the exact same settings(seed, name, world type, etc.)
and the same coordinates in the weird world but it didn't show up. I'm guessing it happens sometimes.
ALSO I have completely no idea how to install MCEdit, mods, that kind of stuff. (means I have none of that)