You cannot get into the Mediterranean without passing through territorial waters.
Grabbing for straws: "Chinese naval escort taskforce visits Tunisia"
http://eng.chinamil.com.cn/CHINA_209163/TopStories_209189/79...
The United States has not ratified UNCLOS, and regularly claims the right of Transit Passage. In fact, this fact is one of the reasons why Iran claims that the United States cannot enter into Iranian TTW while making a Strait of Hormuz transit - because the US has not ratified UNCLOS, their claim is that the US cannot claim transit passage. For the United States (or any Western Nation) to make the claim that China cannot claim Transit Passage would lend weight to Iran's argument, which you can imagine, they would not want to do.
I do not want to make any assumptions around your specific views on this matter - you may hold the opinion that China could not claim transit passage, however I wanted to interject some perspective that:
1. That may not be universally agreed upon 2. Specifically, the United States and it's allies may not make that argument because it would put them in a negative position for other international disputes.