One thing he sort of implies but doesn't directly state -- which I think a lot of people don't know -- is that it's impossible to measure the "one way" speed of light. We can only measure the speed it takes for light to go "there and back". It's possible (but not likely), that light goes faster in one direction than in another direction, and AFAIK, there's no possible way to measure it. You'd think you could do it based on clock synchronization, but clock synchronization itself depends on the assumption that the speed of light is equal both directions.
https://en.wikipedia.org/wiki/One-way_speed_of_light