for activating VCHA on a single host you have to set one advanced parameter for vcenter:
default is true, set it to false
setting works in 6.5 and 6.7, in 7.0 i think its not changed
He doesn't mean "vCenter HA" he means "vSphere HA" or failure-level protection of an ESXi host, not vCenter Server.
No, I don't think you can enable this on a single host because it has certain minimum requirements such as vSphere HA.