That's 1/3 of his holdings. If he wants to sell you may need 12btc to take out his holdings there. "Afraid", that's the wrong word, it's more a decision of my observations.
When price was at 3500? I don't really know what you mean by that.
Are you refering to the last pump that went to 5000? Not sure.
However, I find it very strange that a such large holder will put up a wall like that. Does he really want to stop upward movement to accumulate more under 4k, when he owns 15% or so of the supply.
Or maybe he just not very clever and actually thought that someone would buy down that wall.
It just don't feel to good for me, but I wish everybody else here good luck and I'll be trying to watch how this project evolve