We have only just confirmed that it's not your Pi-hole's DNS providing that information, as that correctly returned gonsaplus as a name for your IPv4 .80.
What's the output of the following command, run from your Pi-hole machine?
That shows the definitions for raspberrypi to be correct - that name is configured for your Pi-hole machine only.
I am out of ideas as to what could be causing this.
As your dig commands have shown, clients in your network are able to receive the correct names.
This would limit this behaviour to Pi-hole's UI only, possibly a glitch.
@yubiuser, I know you to have tested upcoming changes in Network overview a lot - are you aware of erroneous associations of IP addresses and hostnames?
Not in a sense I saw it here. The only things that comes to my mind is this thread:
I also thought that the wrong hostname must come from somewhere - maybe there are some hostname related settings left on the router (even when DHCP is disabled)? What router do you use?