Yes, but there's no discussion so far from CoinBase about the legitimacy of that massive order. They assume it was legit "no sign of wrong-doing."
In the phony, rigged, manipulated precious metals markets, observers often say "a not-for-profit seller showed up to knock prices down today." A legitimate seller would structure his sales out of his own interest and not to wreck the market.
It's still suspicious, and I want to like CoinBase since I was very impressed by the talk from the founder at the recent Ethereum Conference.
Since the crypto markets are not regulated, even if this was market manipulation there's no official regs against it.
Ah, so "regulated," meaning controlled by a third party, such as government, effectively means you can go on cheating the public, every which way to Sunday, without suffering any negative consequences. But in the real world of reputation, you must take occaisonal losses to maintain trust with your would be clients.
Now CoinBase is beginning to change their tune, and make good both with those who appeared to be cheated out money due to the flash crash, as well as those who managed to buy in at low prices.
Sort of like J.C. Penny who said "the customer is always right" which may be a policy though seldom a fact.