The intraday chart of the Nasdaq tells the story. Initially, Powell didn't change his tone and the market liked that. Later though, he said they could hike rates higher if the data stays strong (and he said so unprompted).
"The reality is that we're going to react to the data," he said. "We may well have to do more than what markets are expecting."
The reaction shows just how delicate the market is to Fed commentary.
It's a similar story in FX with cable doing a 100 pip round trip.