How did my submarine end up here?

Hello.

Not sure if it is a bug, but I can't understand how my submarine ended up here. It was on Explore Automatically, I did have Open Borders with Both England and Germany. I thought it was weird and decided to post it here.


http://oi44.tinypic.com/29uqfxv.jpg

A city with water on two opposite sides acts like a water tile as well as being a land tile. It can be traveled through with boats.