Why a 10,000-ton Town looked much larger

Was the Town class's roughly 10,000-ton figure a loaded combat displacement?

No. It was standard displacement; an Edinburgh-group ship was about 10,550 standard tons but roughly 13,000 tons at normal full load.

The familiar 10,000-ton figure was a standard-displacement measure rather than the ship's complete operating weight. An Edinburgh-group cruiser measured about 10,550 standard tons and roughly 13,000 tons at normal full load. The difference helps explain why the hull, accommodations, armament, and protection look too substantial for a literal 10,000-ton combat ship. Treaty-era figures are most useful when the reader first asks which displacement condition is being quoted.