What happened here?

Yesterday morning, I got a message on FaceBook from a neighbor of mine in College Park along with this picture:

What he was showing me was what his water looked like coming out of the tap.  He called the utilities department and they were sending a lab technician out to check it.  He later found out that they had flushed the hydrant on his street and a "gush of something" came over their way.  The lab technician said that the water was indicating a low chlorine level.  The city said to flush the lines - run your faucets, showers, etc.  This included the hot water in the water heater tank.  Eventually, the water cleared in about twenty minutes - I wonder how much water that used and I am sure they won't get a credit on their water bill for the extra water used.

Just another day in our city.  My house was seemingly uneffected.  Has anyone else experienced this sort of thing before?