This is an unusual arrangement, but it makes sense in the larger picture:
The U.S. Navy and the Chinese Navy conducted their first joint anti-piracy drill. A Chinese frigate (the 4,000 ton Type 54A Yiyang) and an American destroyer (the 8,200 ton Burke class Churchill) carried out several training operations over five hours. This included joint use of communications as well as boarding and onboard search procedures. This was done in the Gulf of Aden, off Somalia.
While there was some PR angle to this, the crews of the two ships did get a useful look at how the other side operates. More to the point, it was a useful drill in the event that Chinese and American warships found themselves dealing with the same bunch of Somali pirates. Both sides will distribute what was learned throughout their respective fleets.
All this is part of a trend. China is becoming more inclined to work with ships from other nations patrolling the pirate infested waters off Somalia. Earlier this year, for example, China, India, and Japan agreed to have their warships off the Somali coast coordinate operations to more efficiently protect civilian ships in the area. Chinese and Indian warships have been operating independently off Somalia, while Japanese ships have been operating with Task Force 151. Most warships on anti-piracy duty belong to TF 151. Most of the remainder work with EUNFS (European Union Naval Force Somalia). But some nations continue to operate independently, more or less. In these cases there is always some communication, coordination, and sharing of information with TF 151 and EUNFS.