The Orlando guns' shore-support role

Was the 9.2-inch gun based on an army requirement for a heavy shell that could be loaded by hand?

To an extent. Manual shell handling helps explain the calibre, while the discussion also notes the use of naval guns to support troops ashore.

The 9.2-inch gun may partly reflect an army requirement for a heavy-artillery shell that could be loaded by hand. Guns were sometimes removed from ships during the Boxer Rebellion to support troops ashore, although the Orlandos' 9.2-inch weapons were probably not among those landed. The class's large six-inch battery could also have been effective against destroyers. These uses show why mixed-calibre armament mattered outside a formal fleet engagement.