Is this N. Korea thing more serious than we think?

via Bantay Spratly.

BREAKING NEWS! China PLA troops head to North Korea (DPRK) border as North-South tensions mount
The People's Liberation Army has sent troops to China's border with North Korea as escalating tensions on the Korean peninsula have pushed North and South to the brink of possible war.
The Hong Kong-based Oriental Daily reported Saturday that internet users have been uploading photos of what appear to be PLA armored vehicles and tanks passing through the streets of Yanji, the seat of the Yanbian Korean autonomous prefecture in eastern Jilin province. The city, considered a key transport and trade hub between China and the DPRK, is less than 30 kilometers from the 1,400-kilometer border.
The military deployment is believed to reflect how seriously Beijing considers the the current standoff between North and South Korea. Delegates from Pyongyang and Seoul have agreed to continue talks at 3 pm Sunday local time after the first high-level dialogue between the two sides in nearly a year was adjourned following a marathon 10-hour session.

What do the Chinese know that we don't?

All I'm getting from United States Forces Korea is that they're monitoring the situation.  8th Army isn't saying anything either.  I don't expect much from USMC Forces Korea so what is the deal here?

What has the Chinese so spooked that they'd deploy this many additional troops to an already militarized border?