Gardevoir and Gallade are entirely different species. Gallade is male-only species while Gardevoir can be both male and female. And Gardevoir in this manga is male.
I'm actually a boy."Miss Gardevoir" turned out to be "Mister Gardevoir!"*ba-dum**ba-dum*Will you go out with me?M-Miss Gardevoir...Uh...My trainer likes dressing me up like this.You're a boy?!Shocked into photorealism