What does Genesis 21:32 mean?

A solemn treaty between Abimelech, king of Gerar, and Abraham has just been completed. Abimelech and Abraham have exchanged animals as part of an agreement for their households to treat each other agreeably. Abraham has also claimed formal ownership of the well he dug, and which was taken at some point by men serving under Abimelech. His symbolic price for these rights was seven sheep. This agreement was significant enough that the name of the well's location was changed to Beersheba, meaning "well of the oath" or "well of seven."

Now Abimelech and Phicol, the commander of his army, return home. We're told that Gerar is located in the land of Philistines. These Philistines may have been the forerunners to those who would later plague Israel in the time of Saul and David. Or, the text may be saying that Gerar was in a region which would later be occupied by the Philistines.