I don't need a degree to have knowledge on a subject. It doesn't take a degree to look up the law.
But let me ask you, when's the last time you requested a DNA test from someone before you addressed them under either male or female pronouns? When's the last time you requested a DNA test from someone to verify that they actually were the gender they were claiming upon meeting you?
I can see what he is saying, but I can see what you are saying as well.
Take a MTF transsexual for example. This individual is born male, named "John," and lives his childhood as a boy. He has male anatomy, goes through puberty as testosterone floods his system, grows facial hair, and is a part of the boys' cross country team in high school. In every way, shape, and form, John is a boy. Except, of course, how he feels inside.
Inside, John hates being a boy. When he thinks of his future, he thinks of himself as a girl. He doesn't picture himself walking in to a job interview in a suit and tie, but rather a skirt and heels. When he looks at his own body, it doesn't feel like it is his. His physique, his penis, his slightly hairy (and flat) chest, his facial hair, his deep voice...all of those things feel alien and wrong to him. To him, he is "Jane," not "John."
After he gets a bit older, and a bit braver, he comes out as trans to his family and friends. He starts living his life as Jane, and feels so much happier. Now, living as a woman, Jane is happier. Yet, things are still wrong. Though she feels better about herself, and is happy to have people refer to her as "her," she still deals with fundamental problems that she doesn't like. She doesn't have the breasts she wants. She still has to shave her face. She still has a penis and testicles. She's happier, but not fully happy yet.
Several years go by, Jane saves up more and more money and decides to go through the plastic surgery need to get a tracheal shave, breast implants, cheek implants, and laser hair removal. Outwardly, she feels and looks more and more female with every surgery. Yet, there is still the problem of the genitals. Though she has breasts, a feminine figure, and a feminine face; and though people assume she is biologically female when they meet her, Jane still knows that she will have to deal with male genitals every time she undresses.
A few more years go by, and now Jane has saved enough money for the full sexual reassignment surgery. The day comes, and she is both scared and elated to finally go through with what she has wanted for more years than she can remember. The surgery is a success, and as she recovers she finally feels complete. She feels like the person she has always wanted to be. For the first time in her life, she has nothing about her body that feels foreign, alien, or unwanted. She is a happy woman.
The reason I give that story is to demonstrate how both of you are correct. Tech30528 is correct that, biologically speaking, Jane is still male. Despite outward appearances, Jane still has a set of XY chromosomes. She does not have overies or a uterus. She was still born with a penis, with testicles, and with everything that made her biologically and physiologically a male. Yet, outwardly and cosmetically, she is female. She has a vagina that (although not exactly the same, physiologically, as the vaginas of women who were born with them) functions properly. She can have sex quite pleasurably, she can undress in front of women and not be looked at as anything BUT another woman. To the entire world, unless you got in to her history or DNA, she is a woman.
Did she change her biological sex? No, she didn't. That is an impossibility. Her DNA cannot change. Her chromosomes cannot change. So, yes, tech is correct that Jane is still, in some ways, male.
BUT, does that mean that she doesn't deserve to be socially treated as a woman? Certainly not. Jane has every right to be treated as a woman socially, legally, and personally. You cannot tell that she has male DNA unless, as you said, you give her a DNA test. The sex she was born as, and the sex she appears to be now, are two separate issues. To refer to Jane as anything other than a woman is rude, uncalled for, and entirely unnecessary.