On the one hand, even if the crew was in breach of some UN provision, that is to be solved in the UN, in a boardroom, not in the air. Again, dropping flares on an aircraft is illegal, unprofessional, dangerous and idiotic.
And again, if you read the whole Part (or even point 1), you'd know it specifically enumerates which rights the treaty is regulating does it grant the EEZ coastal state, namely economic exploitation (like fishing and oil drilling), the establishment and use of artificial islands, installations and structures, marine scientific research, the protection and preservation of the marine environment, and the normal rights and duties of any other state.
So the question, in what way do you think flying a helicopter (which is a right of any state in the EEZ) endanger any right of China specifically provided for in this treaty? Did they scare away fish?
EEZs don't protect random made-up rights, only specific ones, and only if those don't infringe on the rights of other states.
To clear it up, which of these do you disagree with?
All states have a right of free overflight and navigation as long as they do not infringe on China's right on oil drilling, fishing and preservation of nature as provided by the treaty part 5 on EEZs.
China has a right to the exclusive exploitation of its EEZ with regard to living and non-living resources, so it is the sole power that can build oil rigs, fish, etc. as long as it doesn't infringe on the rights of all other states for free navigation or overflight.
The AU helicopter was exercising its right of overflight, and did not infringe on China's right to fishing or oil drilling or nature preservation.
Because if all that is true, UN provisions don't justify obstructing the helicopter, and again, even if they did, this would be a diplomatic matter to be settled through normal channels, not by endangering lives through idiotic air showmanship.