Should I say something or not?

Say nothing. It isn't their fault that the cat decided to become territorial. I've had friends who've had cats that do the same thing and they usually resort to locking the cat in a bootroom or bathroom for a few days. Could they improve on their cleaning methods-definitely!! It really sounds like they were trying to be gracious and not bother you. I can tell you are upset by this, but be the gracious hostess and let it go. You really have nothing to gain except hard feelings by making an issue of this.