Why does sabotage not automatically trigger war?

How can blowing up an ammunition warehouse fail to count as an act of war?

The explanation is that the affected state chooses whether to treat the incident as an act of war, with the munitions' ownership offered as a reason for the Czech response.

In this assessment, the affected state's response determines whether the sabotage is treated as an act of war. The munitions are described as not technically belonging to the Czech state, which supplies the reason given for its response.