They might have been willing to risk that in the short run if they felt pretty certain that we would have our hands too full fighting the Muslims to do more than loudly object while they consolidated their hold on Taiwan. Remember, everyone expected a Soviet Afghan experience if we invaded. I doubt they expected more than a "Clintonian" response anyway. After all, we gave a very measured response when they kidnapped our EP-3 and crew.
As for things that raise some suspicion, see below. I also remember reading that some kind of Chinese-made weaponry was found in the caves, but I don't remember what it was and I don't have a link.
See this thread Story Changes -- Macau says five arrested not involved in US Attacks, especially the stories posted in reply #9.
Are Chinese generals misreading Bush over terrorist atrocities? :
The response of Colonels Qiao Liang and Wang Xiangsui, who coauthored authored Unrestricted Warfare, to the terrorist attacks on the US demonstrate my points with striking clarity. Both publicly stated that the attacks are “very likely ... the beginning of the decline of the United States, as a superpower.”
Taliban Commander in Chief : CHINA assisting us in war against US -
Taliban Commander in Chief Jalaluddin Haqqani has claimed that the militia is "in touch" with China, which was assisting them in the war against US.Before leaving for Afghanistan after holding talks with Pakastani officials here, Haqqani, who is also Minister for Frontier Regions, told reporters "China is still assisting Taliban in the war against the United States."
AMID AFGHAN WAR, CHINA SELLS MISSILES TO M.E.
Certainly none of this constitutes any evidence of foreknowledge- but it doesn't rule it out, either, IMO.