That's pretty much it.

The "high speed sync" stuff that modern Canikons deliver is based on lower power/extended duration flash that allows for flash coverage over the entire period of shutter activation.

The problem being solved here is that, unlike leaf shutters, focal plane shutters (above their rated sync speed) do not expose the entire film plane at the same instant: The "closing" shutter starts closing before the "opening" shutter is fully open. Think of it as a slit being waved over the film/sensor.