Make the change to your login to add the PS1 prompt symbol.
Make the change in whichever ONE of the following three files you have; if you have one of the following (visible via "ls -al" command), then use it. If you have more than one of these files, then consolidate the contents into one of the three files. (Multiple different login files are NOT honored.)
.bash_profile
.bash_login
.profile
Pick the display value for PS1 to include something other than the DNS-derived host name your local DNS is serving up, either from your ISP or (more likely) from your gateway router (via its DNS or via its LAN-local DHCP server).
At worst, restart Terminal.app.
Done.
Better, swap the gateway router for a different one, and see if that resolves this.
Here is an earlier (and archived, and slightly stale) discussion of this behavior. (Use scutil to change your local host name with some caution; that's NOT likely a factor here. Definitely look at the gateway-router and the local IP network here; that definitely looks confused.)
And FWIW, Microsoft Windows, Perl and MySQL experience means little here; those are different platforms than is Unix and bash.
And FWIW, the following .profile extract from one of the production servers here contains a PS1 that sets the prompt string (the full DNS host, based on the \H) to red text:
PS1="\[\e[1;31m\]\u@\H $\[\e[0m\] "