World Duplication

When i was casually playing in my survival server with a friend when we went into a mineshaft, we were casually mining.We wanted to look for some chests so we could get some starter loot (since we had bad stuff). when we found a chest in a minecart we were happy, it had a knockback 1 book inside.i took it, then a creeper blew up the surrounding area with the minecart aswell, another knockback 1 book was dropped, we were very confused but continued to look for other chests, when we finally found one we acidentally pushed it, it was 2 minecarts stacked on eachother, that repeated throughout the entire mineshaft.

Seed: 3511788090660722342

Coordinates: somewhere around X= 119 Y= -4  Z= -41