It is confusing at times to read through the old formulas for metal finishes. The terminology used then is different from what is generally understood these days.
Browning was a general term used because the the way to either a brown or a blued surface was through browning(rusting) the metal.

Hot salt blueing was just beginning to be used at the time Angier book was published in the 1930's.
Many of the recipes in the book are from the 19th century and even before. Other than rust blueing at that time, the other ways in general use to get a blued surface on large parts were charcoal blueing (different from carbonia/machine blueing) and a few other types of temper blueing.
Browning, bronzeing, blacking, blueing,,,I'm sure there's more to add.
The term doesn't always indicate the color nor hint at a specific process to attain it.