The player has quit playing. Zepto shows fake gems in these bases so there are enough bases to raid. If they didn't do this, then the game might just say all bases have already been raided and there isn't anything to raid
However, I thought a requirement for a base to show up at all (fake or otherwise) was that the owner of the dungeon has been active some time in the past few weeks or so. Also note that it appears that the owner of the base had a significant amount of gold in his chest (the gif is low quality but it looks like it's a 6 digit number). That would be impossible if he hasn't played in a long time.