I don't think you should put much stock in these things. China regularly conducts military exercises with Russia and have been doing so for a while. They have had similar naval drills in 2013 and 2012. A number of previous exercises have occurred since 2003, sometimes as part of Shanghai Cooperation Organization exercises. For the most part, Russia's incorporation into the SCO was more about assuaging Russian fears of China encroaching on Central Asia. As is their wont with Beijing, the Russians have repeatedly attempted to assume a leadership role in the organization and swing it further into their orbit by bringing its traditional ally India, much to China's chagrin.
As it stands, China has no interests warranting intervention on the side of Russia and they are not going to intervene just because Russia wants them to help. I personally imagine that the Chinese would face minimal opposition from the United States were it to seize the South China Sea, East China Sea, or Taiwan. For one, in all but the East China Sea case, Beijing has incredibly strong territorial claims. With the South China Sea the only party with a fairly legitimate contesting claim is Vietnam and, while the U.S. may well favor Vietnam over China, they are unlikely to do much to help the Vietnamese in their dispute. The Philippines is part of the dispute and a long-standing U.S. client state, but their claim is more limited and far less legitimate. Additionally, only in Taiwan would any conflict be likely to see significant military activity as the South China Sea and East China Sea islands are all rather small and mostly unoccupied. Yet, even there it is likely China already has the capacity to completely obliterate Taiwan's military capabilities and cordon off the island, blocking any potential American intervention.
By contrast, China and the U.S. have many core aligning interests such as in Pakistan and Korea. Although China has some ties with Iran, they are actually much closer with the Arab nations in the region to say nothing of their very close relationship with Israel. There are also much broader economic ties between China and the U.S. than either country has with Russia. I remember when Erin Burnett said several years back how China was probably America's greatest friend to some confused looks, but I would say she nailed it. Most other countries are basically just client states or protectorates of the American Empire, while with China there is some equal footing at present. It is not without rivalry or hostility, but the environment is much more conducive to continued cooperation than renewed opposition. To some extent it was inevitable, though it is as much credit to George W. Bush's handling of diplomacy. Obama has probably done more to worsen ties, though not enough to imperil the relationship.
Russia should be doing more to make China happy as continuing along their current path is more likely to cause a break than a partnership and Russia cannot risk China siding with the U.S. and EU. Doing so would require a change in Russia's traditional attitude towards China, though, and I am not sure they can manage it.
