What does this sentence mean - "He was a capitalist who appropriated the rhetoric of the commune where he had lived"

Solution 1:

To "appropriate rhetoric" is to borrow or use someone else's way of speaking or arguing. In this case, it refers to language you might find in a commune – arguing for cooperation, and the mutually beneficial sharing of labor and resources.

The sentence is intended to show contrast – capitalists don't normally use communal arguments or language. To the contrary, capitalists are seen as the opposite of communists.

Solution 2:

It basically means that he was a capitalist at heart, but he spoke like someone who lived in a commune.

In a commune, everything is shared (think communism), which is the opposite of the ideals of a capitalist. The sentence, as with the others in your example, is supposed to highlight his seemingly contradictory nature.