Your character gets called a trap if they're male but have a femininity at androgynous or below (I think). If your femininity is at or above 50, and your gender is set to Auto, then it'll automatically have your character's gender be female. In this case, your character gets referred to as "Shemale" (which is a weird term, I feel, particularly given that it happens even at max femininity if you have a cock and no pussy).
To have your character be called a trap, you either need to get your femininity to be between 40 and 50 or just select "Gender: Male" from your appearance screen while having more than 40 femininity (which you probably do, because it sounds like your character has enough femininity for the auto-gender to think they're female). The gender selection lets you set that your character is male, and as such, meets the requirements for the trap label.