How is the title of chapter 10 ironic?

After the speech, a man appears with a small brown calf. The calf keeps its head down in the crowd. Little Tree walks up to it. The calf owner convinces Little Tree to buy it for fifty cents. Little Tree considers it a fair exchange, since the man tells him it's worth a hundred times as much; but he's a Christian so will sell it cheap. The irony is that Christian is not being honest.