This would seem to be a new way to monetize hacks. Go short on the market, trigger your fake tweet, wait a few seconds for the flash crash, and cover your short. You could make huge profits this way. I wonder if someone did in this case.
It also started with a first step to "Spread bogus AP press releases".
http://www.economist.com/news/business/21574478-market-softw...
This would be a way of converting that exploit into much more. If you had some experience in finance (or knew the right people), you could easily make millions on a series of trades. Illegal, sure, but this is for a person already used to dealing in very shady corners.
Any trading system used for actual algo trading can do 100 orders/second without blinking. High frequency starts around 1,000 orders/second.
If you wait for verified, accurate news, then anyone who moved before got to move before you. Thus, participants in that market move when they want to accept the risk they want.
It doesn't matter if you verify Twitter with the best security around because markets will and always have reacted to rumor and unverified speculation and news. It's a gamble that the participants willingly make.