Hacker? Ghost? Or just Mod/Admin?

Well there is a server that is fairly new. A little older than 1 month. I go on this server everyday with my friend. The server is getting bigger each and everyday. Some people I knew from when I first came on when the serevr was about 2/3 weeks old. I will hide all names in this story because I don't want any problems. Ok so first there is a person named waffle1. She told my friend Purple of a thing she saw the night before. There was only her on the server. She was in her house fixing it up, when she saw a name bar by her fields. She went out of her house to see who it was, but there was no skin, just the name bar with no name. When she was close enough the name bar dissapeard. Her crops were massed up. So my friend told me of this. Then like 2 days later, when it was only him, he saw the name bar in our spring. our house is in the side of a hill, and we had a spring in side of it. But we live in the snow so it could have just been snow that was hit. I don/t know if anybody else noticed but when I hit snow, for a split second it looks like a small name bar. But no one was on to hit snow. He then told me of this. A few nights later ma and him are talking on the server. we are the only people on. We find a rondome mine, that wasn't there before. We went down and just figured it was hidden or something. We ignored the situation. About 3 nights ago me and my friend, again the only one's on. He goes down that mineshaft to get some iron. we goes home, smelts it then goes back down. At the end of the mine there were6 diamond ore. The person doing this was there with us. Oh before i forget. Before he saw the name bar the first time. we had hints. Me and purp were the only ones allowed in our chests, accept for mods, there was blaze powder, ghast tear and six diamond in our chest. Now back to where i was. We were pretty freaked out. we then tried to dicuss who it could be. soon after a moderator, my favorite, kj came on. COuld it have been him? We keep seeing diamond ranmly appear around our house. neither of us have high enough xp to get silk touch. I have yet to see the name bar. And we have yet to find out who could be doing this.