You are correct. This is widely copy/pasted bad advice and does the exact opposite of what the comment says.
It is not an idle timeout logout at all. Instead, it causes sshd to periodically send probes to the client. This has a couple of effects, most notably keeping tcp sessions "active" and frequently exchanging packets (this can be useful to keep connections through statefull firewalls alive if you are genuinely idle), and to rapidly detect and disconnect a client that has actually gone away.
I think the origin of this incorrect description is the CIS documents. They have the exact same gross mistake in them.
I think the ClientAlive probes are useful and should be on, but it's definitely not an "idle logout" as claimed.
It is not an idle timeout logout at all. Instead, it causes sshd to periodically send probes to the client. This has a couple of effects, most notably keeping tcp sessions "active" and frequently exchanging packets (this can be useful to keep connections through statefull firewalls alive if you are genuinely idle), and to rapidly detect and disconnect a client that has actually gone away.
I think the origin of this incorrect description is the CIS documents. They have the exact same gross mistake in them.
I think the ClientAlive probes are useful and should be on, but it's definitely not an "idle logout" as claimed.