In OS 10.4 Tiger, in order to block UDP traffic, one had to click on the Advanced tab in the Firewall pane and select "block UDP traffic" otherwise the firewall would only block TCP traffic. If you notice in the article, all the open ports are UDP. I don't have a copy of Leopard yet, but given that the author didn't mention anything about the advanced tab I wouldn't be surprised if it's still the same for Leopard and that he didn't make this selection.
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In OS 10.4 Tiger, in order to block UDP traffic, one had to click on the Advanced tab in the Firewall pane and select "block UDP traffic" otherwise the firewall would only block TCP traffic. If you notice in the article, all the open ports are UDP. I don't have a copy of Leopard yet, but given that the author didn't mention anything about the advanced tab I wouldn't be surprised if it's still the same for Leopard and that he didn't make this selection.
Blocking UDP traffic in 10.4:
http://docs.info.apple.com/article.html?path=Mac/10.4/en/mh1242.html