Mathus didn't quite predict that, he was smarter than that.
The fact that exponential growth of population was a rare and short-lived phenomenon in world history (he had numbers from new england or quebec, and knew they were highly unusual) led him to conclude that there must be other forces. The equilibrium population is set by the balance of such forces.
And not just in humans, obviously. Any animal could reproduce exponentially, but the world is not 100-km-deep in rabbits just yet. And this observation was an important ingredient for Darwin.
The fact that exponential growth of population was a rare and short-lived phenomenon in world history (he had numbers from new england or quebec, and knew they were highly unusual) led him to conclude that there must be other forces. The equilibrium population is set by the balance of such forces.
And not just in humans, obviously. Any animal could reproduce exponentially, but the world is not 100-km-deep in rabbits just yet. And this observation was an important ingredient for Darwin.