That is not random. If you self-pollinate a sim with itself, the resulting outcome will always be the opposite gender. No randomness here. The logic of *WHY* this was done this way eludes me, but that's how it is.
Is this true of boolProp-ing any two Sims of the same sex? Will having two male Sims as the parents always result in a female baby, and will two female Sims as the parents always result in a male baby? The reason I ask is that I have one particular Sim... a male... first he was abducted (obviously got a male PT), and he had a girl. Then I used boolProp to mate him with the other male Sim in his household... the result was again another girl. Then I mated a male Sim from a different household with him... and ended up with yet another girl. Is this all a silly coincidence, or is that the way it will always happen?