You sometimes see an overly cautious FA get aggressive about repeating seatbelt announcements during turbulence (on any airline) but I wouldn't call that normal at all, for UA or elsewhere! Many people already have an unrealistic concept of turbulence causing crashes - what a way to alarm people. If there had been some potential for an emergency landing, I'd think that a fuller briefing and explanation, as time allowed, would have been called for. Weird.