Local Multiplayer animation mimicing

I opened a LAN into a newly generated, normal, creative world. I was hosting, and there was one other player who joined. They noticed that in the inventory screen of the creative menu, where it shows the player model, that when I placed or broke a block, their character model would swing the item in their hand as if breaking/placing it. No effect on actual gameplay. When they placed/broke a block, my character model did not mimic their actions.