When you try to access the default IP of a shared server, or the domain which is not exists but dns resolving it to the shared ip , the default action of apache is to show the first domain it finds in the apache server config.
The first domain should be you server default hostname
NameVirtualHost shared ip address:80
<VirtualHost shared ip address:80 >
ServerName host.domain.com
DocumentRoot /usr/local/apache/htdocs
</VirtualHost>
ServerName host.domain.com
DocumentRoot /usr/local/apache/htdocs
</VirtualHost>
