Knowing what I know of Qubes, and reading that post - I think they mean lots of folks are using it for their workstations. Qubes doesn't really make sense on a server, which is how I'd normally read "infrastructure".

Not really for infrastructure though? Still neat.

So their sysadmins don't get hacked.

VPN providers are an annoyance for "collect it all" types. If they have the ingress servers' wireguard private keys, that annoyance goes away. Note that I use the term "annoyance", not "threat"... they sit in that gray zone where it's an irritant but not worth kidnapping people.

I'd bet you dollars to donuts that they're using it to host Whonix nodes for their infrastructure.

Whonix nodes for what?

Ephemeral server instances?