They were on a fact-finding tour about N. Korean refugees and organizations operating in China to help the refugees. After finishing first part of their tour, they were to hold a news conference in Beijing on N. Korean refugee situation, which was bound to be unflattering and draw a lot of international media attention.
The attempt to hold the press conference was in itself a form of protest against Chinese government. It was a success, I would say. It drew intended international media attention. It painted Chinese in a really bad light.
Good that they were able to have a press conference.
The Chinese government might have made a mistake the first time, but it won't happen again. I wonder who is in a Chinese prison over this incident.