Did he say so to them?
Chomas Anach: He said so in front of them, as if he was talking to himself.
What is the meaning of "Nikisi ha'Pa'am"?
Rashi: I am justified to do evil to them. Malbim - surely her second Nisu'in was in public. Others should have protested that a man's wife is given to another man! 1
Perhaps others assumed that Shimshon explicitly said that he will not return to her! A Nochri's wife can divorce herself (Sanhedrin 58b). Are they liable for not knowing laws of Jewish divorce?! And perhaps she lied and said that Shimshon divorced her, or even showed them a Hebrew document and said that it is her Get! Perhaps Shimshon merely made a pretext to vent anger. Alternatively, the Pelishtim were Resha'im. One should judge them to be culpable (Sha'arei Teshuvah 3:218, based on Mishlei 21:12). (PF)