Dustole, what you are quoting is general rules of thumb.
The rule against strategic secessions is not, "If a duchy secedes during a war, it is strategic and must be punished."
A group of disgruntled nobles seceding because they didn't agree with a war in the first place is both a perfectly reasonable scenario and a completely legitimate secession.
Whether or not it is the case, you are sounding very much like you're calling players liars in a misguided zeal to see enemies of your present realm punished OOC.
