In  the movie "Signs," right before the momen the alien appears in
their house, as Mel Gibson is rolling the TV out to the living room,
you can hear a TV newscaster saying something to this effect: "In the
middle east, villagers found a unique, low tech way to defeat the
invaders." What did the writer mean with this line? What did the
villagers do to defeat the aliens?

Maybe he was talking about the water? Since that's how they end up defeating them.

Since the screenplay doesn't provide any details, all we can do is
speculate. It seems likely to me that the people in the Middle East
discovered that water is harmful to the invaders. Dumping water on the
aliens is certainly low-tech.

They hit them with a shoe.