You seem to be applying a pretty strict definition to what is actually an arbitrary term. An act of war can be anything that any nation wants to call an act of war.

So I guess we should probably just use some of the countries involved in the real life case we are talking about.

Does anyone consider violation of airspace by a nations warplanes to be in-and-of-itself an act of war or at least a proactive action worthy of escalation and retaliation? Oh yeah, the United States does. And so does Russia.