It's rude to assume women are bad at video games.
Randall is inviting people to participate in a speed running event, and a person helping him asks Randall to invite some female runners to the event.
Randall wants high quality runners to attend the event.
Randall hosts a competition for men and women and the people with the fastest time are invited to the event.
Randall tells the person helping him that women naturally aren't good speed runners based on his faulty beliefs.
The competition gives Randall's event free publicity making people more excited about the event.
Randall is called for being sexist by the other people moderating the event.