From what I gather, he’s saying the actual number that participated in the Exodus is much smaller than traditionally believed. He brings up the possibility that maybe no evidence has been found of their migration because it’s all been buried in the sand. How do you find evidence of a migration anyway? It’s not like there’s any permanent structures involved. Footprints are bound to have been wiped away by winds, unless they walked through mud that later solidified.
He bases his theory on the presence of Egyptian culture in Jewish way of life, such as the practice of circumcision. He said the Levites were Egyptian expatriates and bullied those customs into Jewish dogma. Wikipediadoesn’t say they came from Egypt. DNA testing indicates Central-East Europe-Indian subcontinent. Furthermore, Wiki’s page for Joshua doesn’t say he specifically led Levites out of Egypt.
I don’t know where he gets the idea that Levites were Egyptian. The Levites are more of a religious order than an actual race, but Jews keep everything in the family.