There is rarely a single reason for why markets rise or fall, but here are some explanations for today's dichotomy:
Tech troubles: Intel and Twitter both came out with troubling earnings reports, dragging down a tech sector that has been largely leading the way in 2018. Apple, Google and Microsoft all finished lower, although Amazon climbed.
Nasdaq's 1.46% loss was its worst in over a month, while the tech component of the S&P 500 fell 2% (overall index was down -0.7%).
Rate rise: The GDP report virtually guarantees that the Fed will continue to slowly raise interest rates. This was already assumed, but perhaps some holdouts only got the message today.
We've previously seen stocks fall after strong monthly jobs reports, for similar reasons.
Meh factor: There is widespread skepticism that 4.1% GDP can be maintained next quarter, let alone in 2019. Particularly given that the figure may, in part, have been inflated by exporters trying to beat tariff deadlines. Add in that most economists had been predicting a very strong Q2 number, and there really wasn't the sort of upside optimism that sparks buying.