Far Cry Primal is something of an spinoff for the series—a stopgap release meant to fill the hole between Far Cry 4 and Far Cry 5. So it’s no surprise to see it recycling things from its predecessor.
As first discovered by the website Gamepressure.com, Far Cry Primal’s map is actually based on Far Cry 4. A source familiar with Ubisoft confirmed to me this afternoon that this was indeed the case, and that the developers of Primal used Far Cry 4's heightmaps—units of topography storage—as a basis for the map in their game, which was released last week. (Stephen really dug it.)
You can see the similarities in both maps: