Hi Delboy,
Sorry I know what you mean about how they are meant to differ - I was getting confused because what I could see at the time I posted that question above was completely wrong (you can see in the photos I attached that they both ended with 3 numbers and this was a first! So it made no sense to me. After I restarted my WIFI network and rebooted the zGemma box (at the same time), the primary DNS went back to normal (i.e. the same IP of the wireless router) and the box IP address also went back to what it was before.
I guess these kind of issues only happen when the internet goes down (which luckily for me, happens only quite rarely).
Out of interest, could there be any benefit in turning off DHCP and manually assigning a static IP?