The fact that most pre-pubertal children with gender dysphoria end up being lesbian and gay adults is based on good quality research.
Your link doesn't show this, certainly not for girls. Only those whose gender dysphoria persists post puberty are likely to grow up to be lesbians.
for natal girls with gender dysphoria virtually all those whose dysphoria persisted into adolescence also exhibited a lesbian identity. In contrast, girls whose gender dysphoria resolved by adolescence were straight.
It is more true of boys, since a much larger percentage of those whose gender dysphoria doesn't persist, grow up to be gay.
for natal boys with gender dysphoria virtually all those whose dysphoria persisted into adolescence also exhibited a gay identity. In contrast to the girls, the boys whose gender dysphoria resolved by adolescence exhibited a range of straight, bisexual and gay identities. The frequency of same-sex attraction in this group of boys is much higher than we see in boys who have never had gender dysphoria (1-2% in general population) which suggests that even when gender dysphoria resolves before adolescence it is still predictive of a gay identity later.
Another study also found similar results.
Using the largest sample to date, with a follow-up mean age of 20.58 years, the study found only a 12.2% persistence rate. 87.8 % desisted and 63.6% grew up to be gay.
If 63.6% are gay, that means 36.4% are not. So although it's quite a large percentage who grow up to be gay, it would be wrong say that all, or nearly all, little boys with gender dysphoria will be gay, because more than a third of them will not, which is a significant proportion. You could say it's 'most' of them, since it's more than half, but I think it would be wrong to say that a young boy with gender dysphoria will 'probably' be gay, because there's a one in three chance that he will not.