He's technically right but he's too much of a dumb dumb to realize he's not making any point here against transgender people and the lgbtq whatsoever. Please stick with me patiently.
Sex is male, female, and intersex varieties. Sex is what you are biologically born as and includes chromosomes. Gender is girl, boy, nonbinary, bigender, genderfluid, agender, etc. Gender can be decided for one's self and changed.
Binary transgender (emphasis on gender) people when they do get surgery are trying to make changes to fix dysphoria (or increase euphoria) by changing sex characteristics and possibly other physical characteristics that are associated along with a gender they do not identify as. However, because chromosomes can’t be changed, it is typically referred to as a gender reassignment surgery or a gender-affirming surgery (calling it a sex reassignment surgery is outdated now that gender and sex are defined as different things even if there are people out there who still see them as the same thing…). But the good news is, transgender people are not trying to change their chromosomes (their sex) so it's irrelevant that it can’t currently be changed by medical science.
Tldr: transgender people, when they get surgery, are trying to change their gender NOT their sex and it's not the gotcha moment Caleb thinks it is because his attempt at being hateful is ill-informed.