While I can't say that 100% of people who identify as trans definitely have dysphoria, the vast majority of trans people I know transition because of gender dysphoria. And many trans people will tell you the same.

Besides, even if a few people identify as trans for other reasons, it still doesn't negate the many dysphoric trans people, whose lives would be very miserable without appropriate accomodation. Hence, the existence of non-dysphoric trans people should not detract from the argument for compassion for gender dysphoria at all.