Wat? I play games all the time on my Windows 10 + WSL2 setup.... which is exactly as I described: Windows running as a guest under Hyper-V alongside Linux.
And you have RDR2 running in that configuration? I mean to run RDR2 in your Windows guest OS that runs under Hyper-V? Because I tried that and it won't run. I could only run it under VMWare ESXi
I believe the point he is making is that the games can run in the native Windows above Hyper-V and then WSL2 / other Linux installs can be run under Hyper-V from the native Windows OS.
As far as I understood it, Hyper-V is a native hypervisor like Xen or ESXi. So if you're using Hyper-V even your Windows is running as Guest alongside any other Hyper-V VMs and WSL2.