Your understanding of culture is so shallow it’s frustrating. Culture is this constantly evolving thing. Cultures mix and transform and create something new.

Part of the reason why the Ptolemies kept a hold of Egypt for the best part of 300 years is their willingness to adopt the traditions of their new homeland. By the time Cleopatra VII was Queen no one (including Rome and her own subjects) saw her as anything but an Egyptian Queen. As for the local Egyptians, the vast majority seem to have been on board these changes and many adopted Greek customs themselves.

Modern DNA analysis suggests that Fayyoum (where these new mummies were found) is actually very homogeneously Egyptian, indicating that throughout its history it was relatively immune to waves of migration.

Whether you like it or not, “ancient Egypt” has been dramatically influenced by waves of its early invaders. These include the Greeks and Romans, but also the Nubian kingdoms in ~1000 BC. The Hittites and the Hixos. The Persians from the east and the Libyans from the west. That’s just how these things work.

As others have said, Egypt is culturally African, Mediterranean, and Arab.