1)
Why did they attribute the victory to "Elokei Harim"?
1.
Radak: It was not due to their Gevurah and multitude. We had far more than them! It was due to their G-d. He had power to help them because we fought them in the mountain.
2)
What is the meaning of "Im Lo Nechezak Mehem"?
1.
Radak: You will see, if we will not overpower them if we will fight them on the plain.