I believe that condition is kind of a decompiler "f-up", as without recompiling it, I never got her pregnant with hundreds of attempts.
But the method recompiled and it magically is possibly, quite fast even. Downside to that too is however that the male natives got pregnant too

Luckily no visual for that, just message popping up.
So unless something changed in the last couple versions, I do believe that this is a bug with the cheatmod (that yona can actually get pregnant).
If the bepinex variant of the cheatmod still allows that, I reckon he just copy pasted and added a check in there, meaning still running the "recompiled" version instead of the original.
Well that, or I was just EXTREMELY unlucky (talking literally after hundreds of attempts) in my normal tests back then. Either of the two.
Either way, aside of a message, it won't change much, so there shouldn't be any actual issues occuring because of it (or atleast not yet I reckon)