These right-wing football fans aren't waving this banner to start a gentle discussion about the differences between sex and gender. They're doing it to be provocative and whip up hate against all trans people (including trans men, women and non binary people). It's a shorthand for basically saying trans people are making it all up, designed to laugh at and try and humiliate trans people, which makes it transphobic / hateful in its sentiment. Intentions matter.