Yes, that is also correct. In the first example, we might presume that this happened a long time ago, and don't know whether this man is still alive or not. Both the fact of his not being wise and the thing which he did are fixed in the past. Your alternative example gives us more information because we know that this man is alive, and that he isn't a wise person. This sentence is a mixed conditional: "..he wouldn't have done such a foolish thing" refers to an event in the past, while "If he were a wiser man" refers to the constant fact that he isn't wise.