Someone In Golden Armor

Hello, I dont know if this was mob or a player. Im Gonna Tell You The Story (may be short).

So I Was In Menu, I Clicked Singleplayer And Made World Called New World, i didnt change name. so it was loading. i started world and started my first survival. i didnt even know how to craft a pickaxe or a sword yet because i was a bit new. i tried surviving but it became dark and i had less food in hunger bar, it was probably because i forgot to kill some animals, or i eaten food too early or i didnt even find an animal to kill, zombies and creepers were running to me i was escaping, i had only 2 or 1 heart left. when i came to a water and i seen someone in golden armor not looking at me and showing me his back. he seemed like he is ignoring me, he was holding sword like an player. i was confused if it was a skeleton because skeletons can have even swords and armor too. i encountered sometime skeletons with armor and sometimes a sword and armor in their hand. there we're some squids on water. i was scared they would kill me so i placed some woods to get to the guy. when i came closer to him he turned to me like a player and killed me with diamond sword or other. i wasnt even afraid but confused. i respawned and i tried finding him and i couldnt find him again.

(Sorry if there are no screenshots of him because i didnt have anything to screenshot with, but this really happened. Believe if you want at your own risk. and before i end writing i didnt have second encounter with him. Sorry.)