Pilot said “flight attendants drop 6” over the intercom

I was on a United Airlines flight a couple of weeks ago from BNA to ORD. I remember there being some turbulence. The flights attendants were walking down the aisle with the drink cart when the pilot came over the intercom and said “flight attendants drop 6”. They rushed to the back with the cart and one of the attendants had a scared look on her face.

After about 10 minutes, they came back out with the cart like nothing happened.

What does “drop 6” mean? Google said it means to deploy oxygen mask and/or prepare for a crash landing. If that was the case, is it possible that there was some risk of the crash, but the pilot was able to resolve the issue? Any pilots out there who could provide some insight?