An anonymous Twitter account sent markets reeling today

Wasn't it more that Fox Business elevated that tweet without doing actual journalism? (essentially what the Fox news properties do all the time because facts don't matter to them anymore)

Who made the trades that took advantage of this?

Not in this case. Fox News didn’t initially report it as fact, but rather the claim seemed to stem from a misinterpretation of Hassett’s interview.

But then CNBC flashed a similar headline (without unpacking it as not what Hassett actually said, and then Reuters picked it up, citing CNBC. And markets spasmed 3.5%.

What Hassett had actually said, for those who missed, was 'Trump's gonna do what Trump's gonna do.'