1. The reason they didn't pre-announce the quarantine was that it would defeat the purpose -- people would rush to leave ahead of the deadline.
2. Guy being kicked out of his college dorm: they had so many cases that they needed more space to isolate confirmed cases. They may have built a pre-fab hospital in a week, but that was nowhere near the capacity necessary. A college dorm is one of the better buildings if you need a building to turn into a makeshift hospital immediately. You've got a bunch of small individual rooms, kitchen facilities, and common areas that can be repurposed. The government determined that it was necessary to appropriate the building for the good of the city and did it.
And look at where we are here in the U.S. We had a two month head start, and we still can't do widespread testing, the virus is spreading undetected. China was strongly criticized for providing unreliable numbers, and here we are, now the CDC has simply stopped providing state by state data on testing, and stopped providing a total count of tests done. It's truly shameful, and I pray for the health of people in this country, especially older people.