I searched and looked at pics of that colocasia and it looks nothing like them, the leaves are thicker, and it is alot smaller and doesnt seem to be getting any taller. Are you posetive thats what it is?
Well, I will say 90% positive. With out having it in my hand, I can't say for sure. Invasisves tend to be highly plastic species, so things like leaf thinkness or the hieght of the plant may not be good traits to identify by.
With that little bit of color along the mid rib and at the point where the petiole meets the blade, it may not be. Was it growing in shade? You said the leaf was thin. Is it extremly thin, like a sheet of notebook paper? If so it could just be a stunted Caladium. They tend to be presitent this far south, so if they have ever been grown in your yard one could pop up out of the blue many years later.
Just rember, leaf shape with a lot of Aroids varies with age and environmental conditions.