Na documentação do Suporte ao host virtual baseado em nome do Apache:
Name-based virtual host resolution only chooses the most appropriate name-based virtual host after narrowing down the candidates to the best IP-based match. […]
When a request arrives, the server will find the best (most specific) matching argument based on the IP address and port used by the request. […]
The default name-based vhost for an IP and port combination
If no matching ServerName or ServerAlias is found in the set of virtual hosts containing the most specific matching IP address and port combination, then the first listed virtual host that matches that will be used.