ComputerNamePhysicalNetBIOS and "Current Host Server" shows different machines

I have an SQL instance (2008 R2) on a two node (say names X and Y) windows server cluster (Windows Server 2008 R2 Enterprise).

Server Manager on both nodes shows 'X' as the 'Current Host Server'.

However, when I run ServerProperty('ComputerNamePhysicalNetBIOS') it returns 'Y' which should be the current active node.

If I RDP to the SQL's IP, it indeed connects to Y.

Which one is the correct one? Why does Server Manager shows X as the active node?

Also, ServerProperty('MachineName') returns neither X nor Y but 'Z'. Z is the name of neither computers. What does it represent? According to BOL for ComputerNamePhysicalNetBIOS (which returns Y as above): "If the instance of SQL Server is in a failover cluster and you want to obtain the name of the failover clustered instance, use the MachineName property." Then, why does it return Z?