Normally when someone is logging on it says  "F96T12 DD VHO | 6:46:19 | PM Logging into the forum"
But when a guest logs on that same guest stays for like 5 mins
Why is this

Could be a bug that they might need to fix.

When anyone goes into the login page he is still guest. So he is a guest logging into the forum

Maybe when he logs in as user, the systemn still remembers the guest in the login page separately from the logged in user, so the guest stays there for 5 min (as it shows users active in the last 5 min)

You can test this posibility : Come as guest to the login page, and from another device identify yourself. Then log in and from the other device see if you are still there in the list as guest

Maybe he really is a guest that stares at the username/password fields and leaves... Maybe some bots trying to pick passwords to accounts (so dont use 12345 passwoeds)