Naturally spawning rails without mineshaft underwater

So I was digging around the ocean about to make a little glass hut in creative. I broke some a piece of sand but it spawned with nothing under it so it fell but for some reason there was minecart tracks and they broke when the sand fell. (I too am very confused)

 

I took a picture with XRay to show they are in the middle of nowhere, no mineshaft.