He didn't get grilled at all. Instead senators (not the Fed) asked him stupid questions like "why I'm I seeing ads about chocolate?" and "how do you sustain a business model in which users don’t pay for your service?". Their questions were shit and his answers were shit. Plus with less than 5 mins each to ask questions, they really had no time to dig into the important stuff anyway, despite touching on some of the important issues. The whole thing was a complete farce.