It's been growing since it went up. When I first saw it, it about 10k. Before that, it was a 5k wall that didn't seem so out of place at the time.
I think what people also have to remember when dealing with these types of 'walls' is that it is very likely that more then one person made asks at $6.00. I assume you are using Clark Moody for your real-time data? Clark Moody combines bids of the same value so that they look like huge walls placed by one person while in reality it is simply a price point which people chose to sell their BTC at. Think about human psychology, we like nice round, even numbers because they are aesthetically/psychologically pleasing; which is also why when I make a bid or ask I use this fact to my advantage.
While fake walls can be a product of manipulation, I believe that in most instances it can be explained in other ways....anyways just my 2 cents.
The thing is, it can, in many cases, be put up, or removed in one click. So unless they have impeccable timing, they are usually one player. At least the majority of said wall.