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the Mac is not sending that out in the request.

I could be wrong about this, as I haven't analyzed actual arp requests in ages, but from the article it appears the arp requests are unicast to the (at least in the example) cached MAC for the gateway.

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Ah, after a closer look at the original article, I see that now. Curious that Apple would choose to unicast those requests.

It does this to verify that the DHCP server has the same MAC address as the one that it remembers. If the server that it remembers isn't present on the current network, the unicast packet should be ignored.

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