Etymological research is rarely cut-and-dry. The authors are aware of this, and the quotation is being held as a counterexample to "the conventional wisdom that

Etymological research is rarely cut-and-dry. The authors are aware of this, and the quotation is being held as a counterexample to "the conventional wisdom that the word “southpaw” originated “from the practice in baseball of arranging the diamond with the batter facing east to avoid the afternoon sun. A left-handed pitcher facing west would therefore have his pitching arm toward the south of the diamond.”" The article goes on to point out that southpaw was almost definitely a boxing term before it was given its baseball "etymology".