Why Panzerschiffe became pocket battleships

Is a book wrong to call the German Panzerschiffe pocket battleships?

Not necessarily, because the label is common, but Panzerschiff means armored ship; pocket battleship was largely a British press invention rather than the literal German classification.

Panzerschiff literally means armored ship and does not itself require a battleship classification. The familiar pocket-battleship label came largely from British press usage and then persisted in historical writing. The exchange helps readers distinguish an official category from a memorable foreign nickname.