That's the definition of it.
> You're correct that it's possible that gender dysphoria might be a downstream effect of society. Namely, we are an extremely gender-segregated society. I'm not saying that it's that simple and all transgender people would disappear if we live in a society with no gender roles or expectations, but certainly they heavily feel the pressure of those gender roles and expectations.
I don't think this is the case. Strict gender roles might make trans people's dysphoria worse, but it's primarily about a strong desire to be the other sex and not have your current sexual characteristics. Even in a world where everything is unisex, a trans person would still feel that discomfort - for a trans girl/woman, that you wish your voice were higher and not like a man's, that your face seems alien, that your genitals are wrong, literally anything sexed about the human body. It's orthogonal to whether a man can wear a dress or makeup. Not all trans women are even that feminine. And if it were about gender roles, then you'd expect more trans women to exist than trans men, given "there's truly only one way to be a man, although there are multiple ways to be a woman."