I am assuming that the wall is caused by one entity. Such entities capable of selling
BTC30,000 exists, but they are few in number. I would put the figure at 30 potential sellers.
The number goes much lower if we consider the risks involved in selling so many coins in Bitstamp.
It is hardly a forced sale, because it is unlikely that such a position would have been financed by debt such that it must now be sold at a loss, and if this were the case, a wall would likely not be the way to realize the value.
It is hardly a panic sale, because the people with 30,000 are not prone to panic selling. If they were, they would have had ample opportunities to show their panicky nature in 2011, 2012, 2013 and 2014. (And people buying in 2014 who are prone to panic, never had the $20-$30 million needed to begin with - panicky people cannot amass so much money).
I can only conclude that it is a scare wall, intended to bring the price down for accumulation. It is used during weekend when no new money is coming, mitigating the risk for an outright buy. In case of nibble, it can be safely pulled.
No matter who has already bought so many and wants to buy more, I see it as a natural and inevitable development in Bitcoin's way to be more widely adopted.
By the way, I have a castle for sale for bitcoins. Serious inquiries to PM please