[Accujack]

>What if it were a Chinese mine that they hit?

Laying a minefield in international waters (from the point of view of everyone but China, anyway) is an act of war. It's not necessary for there to be any interpretation or misunderstandings at that point, it's pretty much the same as if the Chinese fired ballistic missiles with real warheads at Taiwan, or engaged foreign navies in the South China Sea with swarms of anti ship missiles. At that point, the war has already started, so no one would do that unless that's what they wanted.

Which is why China hasn't placed any mines there, and your question doesn't make sense.

[xxpor]

Isn't flying jets into Taiwan's ADIZ without announcing yourself also an act of war, technically? The Chinese do that all the time.

[Accujack]

Technically, no. If they flew in and attacked, that would be.