I think they know they were Philistines from the artifacts buried with them—not the bones.
Sampson slew 6,000 Philistines with the jawbone of an ass. Hitler slew 1,000 times that many Jews with the same tool.
Interestingly, they found these bones 7 years ago. Must be a lot of work. I was always under the impression the Philistines were islanders - probably from Greece/Italy area and migrated east to what is now Israel and Syria. I’d have to look it up to see if it’s the exact same time period, but there was a period of drought and hunger that forced the people of the southern Med region to relocate, causing of course conflict with other tribes/nations/people. The artifacts found may link them to other findings, but afaik there is still no written record directly from the Philistines - only records written by their enemies like the Israelites and Egyptians.
They knew they were Philistines because of the clear indications of bad wine/food pairings, and a total lack of appreciation for the finer aspects of bouquet, color, and finish in a proper wine. To say nothing of their totally gauche choice of footwear—really? Sandals after Labor Day? Really?