There’s more to being male (or female) than just your genetalia.
As we grow, our gender affects how our bones, muscles, etc grow, and how fat is distributed throughout the body. Because of this, equation sets will typically use different formulas to estimate body composition based on gender.
When entering data for a person, you should always use their biological sex / gender, regardless of which gender they currently self-identify as.
Posted in: BC 1.x - BC 2.x, BC 3, BC 4, Other Software, RJL Software, Validity of BIA