The link with the quote doesn't work for me but there are two different things when we look at the ARP request:
- Destination Address
- Target Hardware Address
These are two different things...the destination address is found in the layer 2 (Ethernet) header and specifies where to forward the frame to, it's set to FFFF.FFFF.FFFF (broadcast). The target hardware address is found in the ARP header and since it's an ARP request, we don't know the target...it is set to 0000.0000.0000.
If you capture an ARP request with wireshark then you'll find both values