I think the point is that you wouldn't call a stereotypical goth geeky so, if one is, the contrast is that much greater. It's no surprise to find out a person who spends all their time playing video games, reading comic books or playing dungeons and dragons is geeky, but when a goth, who is supposed to shit bats, fart wolf howls and be an unfeeling corpse person who just doesn't care and is above it all (kinda like cool kids in the 90's

), turns out to have a geeky side people usually get confused.
Personally I don't have that much of a secret geeky side, but I do have some embarrassing girly habits that I tend to hide. Like crying while watching the sappiest romcoms you can imagine or having a bedroom that looks like it belongs to a 4 year old fairy princess and not a blacker than death goth girl