As Vortex says that ain't a Easter egg its just collectible content in the game to find :) But info for you the Moon had a 0/5 golden chests, so am guessing all locations will including Mars and Venus will have too, hopefully meaning all will have more better rewards for finding the 5th chest (hopefully Better Sparrow with cannons because they get faster, Stronger and Strafe Left and Right functions for sure). Its possible to get the Pike in the campaign mode that has guns on it (was in the Ship graveyard area if you waited around long enough, 3 enemies riding them and found doted around on the Moon) hope that helps Guardian :)