If we are going by classic terminology, the trap requires that you are immediately attracted to it as a female, in the initial instance, before the ultimate reveal of their magnum dong. Here, it may only be gay if, and only if, you find them attractive after you find out they are a male. The precedent of your arousal by the feminine features indicates a clear, indisputable heterosexuality, regardless of the objective, physical reality of the trap itself. The subjective perception at that point is that this is, indeed, a female. A member of the opposite sex. Stimulation is unavoidable, in the circumstance of such an encounter, if the individual themselves are not gay af. Unless this stimulation continues past the point of the revelation, and perception no longer remains that this is a woman, then it is reasonable to assume that this man finds arousal within male genitalia, and is therefore an obvious homosexual. And this point is the focal, crucial moment for us to determine the sexuality involved, as once it has occurred, the trap itself has emerged, and is therefore, by definition, no longer a trap.