Here is one passenger's account of what happened - it is certainly described as a "nose down" event. Stall recovery?
"Rod Williams II said he was sitting near the back of United Flight 1722 with his wife and kids on December 18 when it suddenly came down. The plane, which had been headed to San Francisco from Hawaii when it found itself in an intense storm, proceeded to go into a 'dramatic, nose-down' dive for about eight to 10 seconds, creating mass pandemonium in the cabin, Williams said."
"About ten minutes later, and there was an announcement that assured the passengers the event had passed. "Someone from the cockpit got on the intercom and said, 'Alright, folks, you probably felt a couple G's on that one, but everything's gonna be OK,' said Williams, who is the first passenger to provide a personal account of the incident. ''We're gonna be alright,'' Williams credited the United staffer saying."
https://www.dailymail.co.uk/news/art...es-ordeal.html