This monitor tracks the internal vCenter events for linkstate down/up per host physical NIC. Check the event description via Health Explorer to confirm the status.
Note that this monitor does not generate an alert by default, as the NIC status is tracked via monitoring the virtual switch or distributed virtual switch that it is connected to. The Veeam MP for VMware monitor for dvSwitch will generate a single alert with rolled up status of all connected host physical NICs.
See the VMware Online Documentation for more information on VMware vSphere, in particular: