The original ad was posted with the title "If you enjoy mathematics, no prior work experience needed" and a really intriguing body that alluded to interesting work that they'd train you on. He asked if we had any questions for him, if we could get to his office (i.e. were in commuting range), what was interesting about us, and finally asked for a brief summary of our work/schooling. He specifically didn't ask for resumes, although a lot of people sent them to him (and then dressed for the open house in a suit, lol) because of how ingrained the standard motions of hiring are among candidates.
He followed up to every email with a personal response where he sounded like a human being, and then told candidates that there'd be an open house and then we could decide if we wanted to keep on in the process.
I imagine some people shied away because of the time commitment of learning what we could about a new, weird language over a week, and there were some things that didn't work very well because of how different his hiring process was from the norm, but it was enriching and fun in the end.
The big thing that might have worked in Brooke's favor was that this all took place in 2011, when the job market was even worse than it is now.