If we're to assume that discontinuation of gender-affirming hormones means those individuals no longer felt they were transgender or experienced gender dysphoria, then around 30% is a remarkable proportion of people who desisted. I can't get full access to the article yet so I'd need to read in more detail to see how accurate that assumption is likely to be.

For context, remember this study involved people who had already started hormone treatment. A 2016 review paper which summarised all the studies at time on rates of persistence of gender dysphoria among childrenwho have not already transitioned socially or medically showed that in each study, the majority of children 'desist' i.e. grow out of gender dysphoria through adolescence.

Gender dysphoria in childhood https://pubmed.ncbi.nlm.nih.gov/26754056/

In contrast, studies show that children who take puberty blockers almost always go onto take cross-sex hormones. It could be that these children just represent cases of 'strong' gender dysphoria. It could also be that taking cross-sex hormones and gender affirming care start children on the path to hormone treatment, when they most of them would have naturally resolved their gender issues over time.