Yeah, I agree.
It's a bit ambiguous with the mod in terms of whether the stat "Pregnant +1" is confirmed pregnancy or just means increase in likelihood to get pregnant.
With Mida, we get that stat several times in a row, so we get a good idea that she's most likely getting pregnant (than not), but with other girls who only received that stat once, it could be as you said.
Though I do find it a bit weird that with Katriona, we have 2 times we cum inside her (one time it is a choice, other time I think it just happens as a scene without choice) that we didn't even get the stat even once.
Probably same for other girls as well.
I mean, if I choose to cum inside all girls every single time, how does the game choose which girls to give this +1 stat to and when?