Virtual server question

Noob question. After recently switching out a router, We were having some issues with our virtual servers. We have a physical server with a virtual host and 3 VM’s on it, but we could only ping one of the VM’s, the host and other VM’s were unreachable. I’m shadowing an analyst and it was determined that the issue was physical cabling which was misconfigured after the router switch. I’m curious if two things:

1. How could one of the child VM’s be reachable if the host was not able to be pinged and
2. How is physical cabling involved with VM’s, I always assumed there was one Ethernet cable attached to the NIC on the back of the server and all switching done for the VM’s was virtual