Out of my own curiosity what is the definition of a kingdom being in hostile?

Example: Kingdom A attacks Kingdom B. Kingdom B does not retaliate. Kingdom A tags up as "Hostile to Kingdom B". Kingdom C attacks kingdom A.

Did Kingdom C commit a "double hostile" on kingdom A?

I would think that a kingdom isn't double hostiled unless 2 kingdoms are hostile to them. In the case above only kingdom C was hostile to kingdom A, because kingdom B did not retaliate. HOWEVER if then Kingdom A sees kingdom C attack kingdom B, and Kingdom A decides to take some revenge on kingdom B, that would make Kingdom A the culprit of a double hostile, correct?