I honestly think you overshot the point by a few degrees.
However your friend identifies is valid, whether they decide they’re genderfluid, transfeminine, nonbinary, or otherwise. You don’t get to decide that their gender identity is bullshit because you don’t know what’s going on in their mind. Take a closer look at TransStudent.org’s Gender Unicorn.
Gender is more complex than just crossing one’s legs or not, dressing in a particular manner, or enjoying certain things. You are correct that behavior and presentation do not equal gender. Gender is how you feel, and whatever road your friend takes to figure out how they feel about their gender is entirely valid. There is no “going too far in the other direction.” That’s an awfully flippant way to dismiss someone’s journey to understanding how they relate to gender.
The whole point is that man, woman, nonbinary, genderfluid, etc are labels have little to do with our sex or gender assigned at birth. You are still trying to contextualize your friend’s gender based on their genitalia when you call their exploration of gender “bullshit” and insist that they can still enjoy what they enjoy and be a man. It misses the point.
Your friend is probably not a man, even though they are sexually male.
The point of this essay is that we come by labels like transfemme, nonbinary, transmasculine, genderfluid, etc because society tries to tell us whether we are a man, woman, or otherwise entirely based on our genitalia. Gender and sex are separate concepts. The way we move through and are treated by society is largely where we get our genders. Isolating the concepts of sex and gender from each other is the ultimate goal here, allowing all people to self-identify entirely free from cultural precepts.
What I think you’re missing from my piece is that trans people are transgender both because they are trans and because we are treated differently from cisgender people. We need these words not because we are fundamentally different, but because we are harmed by society’s staunch belief that genitals are destiny.
As a trans woman, I didn’t “take it (gender) too far in the other direction.” I spent years confused and suicidal because I was constantly told that my destiny was to be a man — that my sex and gender assigned at birth were not mine to dictate. Coming out as a transfeminine, nonbinary woman was necessary to being myself, because I will never be a feminine man. I am a woman. The way I move through the world is as a woman. The modifying word “transgender” and “nonbinary” merely add context to my womanhood.
In a perfect world, I would just be seen as a woman and wouldn’t have to fight so hard to be seen for who I am, but I have been constantly abused and mistreated by others for being myself. This reality makes the “trans” label extremely important to me in not just how I access the world, but also in receiving life-saving, medically necessary gender-affirming medical care. It’s necessary because it’s necessary.
There is no “going to far” in the other direction, because the sex-obsessed gender binary is what’s bullshit, not those who find that they don’t fit well into that binary created by those who have set the status quo for generations.
Your friend is valid in whatever gender they find makes the most sense for them, even if that means they are fluid or have no gender at all. I hope you remain patient with them and never tell them that their journey is on a path to “bullshit.”