I rarely fly [United], so maybe this is normal protocol, but I don't recall ever hearing it before.

On our way from LAS-ORD the other night, the ride started to get bumpy about 30 minutes before our scheduled landing time. A FA (female) came on the mic with the normal "the captain has turned on the fasten seat belt signs due to expected turbulence, etc."
About 3 minutes later it started getting more rough. Bumpy, but nothing too out of control IMHO. Just then the FA (male) comes on and says they will be picking up service items very quickly, so please cooperate. No biggie, but he seems a little frazzled.
This is what struck me as odd. After he put down the mic, then picked up a few rows of garbage, he hustles back to the mic and says "Please remember that in the case of an emergency landing, leave all your stuff and exit as quickly as possible" and hangs up the mic.
You could have heard a pin drop in that plane! The people next to me were returning home from their honeymoon and were holding each other, welling up in tears.
I quickly plugged in my headphones and listened to ATC. Nothing unusual. In fact, we had cleared the turbulence and landed without any incident.

So my question is, is that a normal announcement, and I just never noticed it?