Why does mesh behave like mirrored in Edit mode without Mirror modifier? This is probably a very simple question, but the Mirror modifier keeps mirroring my model though i've applied/deleted it.

I read somewhere that I have to disable symmetry lock, but I'm assuming that only works in Sculpt mode which I'm not using because I'm trying to make a low-poly model. I'm not entirely sure why this is happening because I've done it before and I didn't face any problems.

If i can get some help that would be great!
That could be this "X mirror":



You find that in Edit mode, on the Toolshelf (press T to toggle visibility), under the Options tab.