Plugin #20094 attempts to guess if the target host is indeed a system run under VMWare. It does this by looking at the Ethernet address and checking to see if it is one allocated to VMWare "hardware". To do this, the plugin looks in the knowledge base of the scan to obtain the Ethernet address.
Originally, the MAC address was either obtained by a local ping (plugin #10180) or from scanning a Windows host. Tenable recently added a change to the SSH login process such that the local MAC addresses are also populated into the knowledge base. This means that a non-Windows VMWare hosts not on the local network will now be detected as a VMware host.