He was proven wrong in that what he predicted didn't happen. That's wrong enough to be called "wrong", no matter how reasonable his reasoning was at the time.

And you missed one point with your discussion of linear and exponential. Agriculture wasn't linear. It wasn't even in his day. There was improvement in per-person output since, say, the 1400s, and more since, say, 2000 BC. There was a technological component even then.

So population wasn't exponential, agriculture wasn't linear, and what he said would happen didn't happen. How much more wrong does he have to be before you are willing to call him "wrong"?