I think HM and awardees make up the top 30% of applicants and based off of a recent reddit thread "comments from a GRFP reviewer," the NSF chooses who gets the award from the top 30%. They probably apply their agenda here to diversify science or something... though that isn't something we're privy too. I got HM too and definitely wished I received something monetary...even like $200 to use for our next conference would have been nice...