Every computer with TCP/IP stack uses DNS ... server + users computers.
Most read host file first before checking DNS servers.
On your workstation ... it has a host file and it can be used to spoof ... how easily that is done depends upon platform ... easy to do on a mac ... /etc/hosts is an ascii file and can be edited via terminal as superuser to make that IP -> FQDN entry. Not so easy on Windows ... which is typical of that platform.
Your Ubuntu has /etc/hosts and it can be used the same way.
Unfortunately, you have 'Plesk' which is highly protective and in this case gets in the way.
I practice what I preach ... have used FQDN 'spoofing' ... but don't use Plesk.
'SoS', Ken