I think "geek" encompasses many different types of people. In my last job I worked with a bunch of software testers and developers, all of whom would probably be considered geeks.
I found they were quite varied, though. Many were potbellied and geeky looking, but others clearly worked out, a bunch of rode motorcycles. My coworker, who looked like the classic geek--fat, balding, glasses--was a really cool guy with 4 kids and scads of grandchildren.
Some people start in other fields and end up in "geek" fields. And/or have hobbies that are more right brain.
So, what attracts "geeks" likely varies as much as they. Except for the usual guy things, of course.