That page is just a example.
The fw rules depends on if you configured the radius and on what meraki dc you are hosted etc.. If you dont have a radius server that rule is not present under help> fw info on your dashboard.
Yes source is <you networks ip> (management ip from switch,ap,mx) dst =radius ip
Not sure why i says inbound (that would asume the radius server always initiates the session, im not sure about this), i would allow it both ways