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/etc/hosts is not the only place to set/configure the hostnames of hosts. A valid public DNS record could be another resolver for your hosts in case you have defined your hosts' hostname with a public DNS provider (A or CNAME records). However, Linux systems usually resolve the hostname as per the order of the resolver in /etc/nsswitch.conf file.
There is a lot of standard DNS commands that exam your hostname resolution, like: dig, host, nslookup, whois, and many else..