Okay... often times characters "appear" to be flying, even when they're on the ground. It's a glitch in the game, but the people aren't actually flying. People think I fly sometimes. It happens when you warp onto a half block (slab) and glitch to be halfway inside the block below it (only your head sticks out). You jump out, and viola... you're on the ground, but people see you as .5-1.5 units above the ground (anywhere in that range, I find it varies). As well, there's been many problems with this person (the one you're reporting). He's been checked out many times, and hasn't been found to be hacking (wtf I typed hacking a billion times and kept saying backing, I'm fail).
People assumed you're a guest because these are your first two posts. In your application you agree to be an active member on the forums (I bet 50% of people who apply don't even read this, just answering yes to every question).
It is also improper to claim someone as hacking. What if he is a member and you're on his land, and he's trying to get you out? Have you thought of this? He never typed to you, so how can you tell he's a guest? There's no compelling evidence in this case as to whether he's a member or a hacker, so please don't call him a hacker without sufficient evidence. That is a serious claim.