These are stolen bitstamp coins being dumped, probably on btc-e or huobi, in turn causing bitstamp to crash. The timing is suspect, to say the least.
If thats the case the drop will be temporary, 18k coins isnt much in the grand scheme of things.
I think it is only a trap , I will not dump my bitcoin ... instead I'll buy some bitcoin. Come on guys don't fall into the trap.