1)
Why did they say "you know that Pelishtim are ruling over us"?
1.
Malbim: If Nochrim say "give to us one of you, and we will kill him", they may do so only if he is Chayav Misah [according to the Rambam], or if he pursued many and endangers Klal Yisrael. Then they may hand him over, even if the Nochrim did not specify whom they want. You are endangering us!
2)
What was Shimshon's answer?
1.
Radak: They did evil to me; I am entitled to do evil to them - "Ka'asher Yiten Mum ba'Adam Ken Yinasen Bo" (Vayikra 24:20).
2.
Malbim: I did not think that my acts endanger you. It is matters between me and them. They do not pertain to Klal [Yisrael].