Australia claims they were flying there for surveillance to enforce sanctions on North Korea. UNCLOS stipulates what internationally lawful uses of the sea are (including freedom of navigation, overflight), and it’s difficult to argue that foreign surveillance falls under that definition. Notably, surveillance does not fall under overflight, as overflight stipulates that no activities are conducted over the flyover that are not related to the flyover itself.
Your claim is that military surveillance is an internationally lawful use. That’s insane. Your interpretation would allow Chinese and Russian aircraft to surveil within 12 miles of the US mainland, drop maritime survey beacons outside of key harbours (to spot submarines and map out the harbour), and do acrobatics within view of major US cities.
Again, dropping warning flares in front of an aircraft to intercept is standard policy. It’s not even worthy of mention most of the time, and it’s described in FAA rules.