The Philistines mentioned in Genesis are not the same as the Philistines in Judges through Kings. The earlier group had Semitic (ancient Near Eastern) names, such as Abimelech, and they followed Canaanite culture.
The later Philistines were likely from the Aegean region (near Greece). They had different customs and culture. They seem to have come to Canaan by sea around 1200 BC, during the time of the judges.
Because of this, the name Philistines in Genesis is probably used to describe the earlier people of the region in a way that later audiences would understand.