That is a ficticious statement. When I first started breeding Traditional Siamese, our litters did tend to run boy-heavy. However, the last year or so, we have been mainly having litters like 3f/1m, 4f/1m, 4f. But then we did have the one litter of 6 males and 2 females in there too!
So, if you think you have more girls than boys, there's nothing wrong with that. Just love them and enjoy your time with them!