You might want to read up on freedom of navigation. It's what China uses when it's vessels sail through the Vietnamese, Malay, Filipino, etc, legal jurisdictions in the South China sea. Russia does not own the Black Sea and NATO allies Turkey, etc allow NATO vessels to patrol their waters. The vessel you mentioned is in fact on NATO business and entitled to be there. You might also ask what 2 PLAN frigates where doing in the Blacksea, unless the Chinese have drawn an imaginary dotted line through the area and are claiming it as Chinese territory. They do have form.
