Actually, they have a legit excuse: he's attempting to politicize the Olympics during the games. While it's impossible to avoid all political issues (as we're still seeing right now), Beijing wants to keep it at a minimum.

Many of these Darfur activists have ignored something important: China has approved of a UN Peacekeeping resolution in the region and even committed several hundred troops to the effort, as well as provided aid (monetary and labor) for the construction of schools in Sudan. The only thing they haven't done is condemn the violence verbally, which has (mis)led people into believing they're supporting the violence.