I visit Android Market almost everyday, but never saw this till today. Looks like Google is trying to improve the search experience with filters on the Market. It is a nice touch, but it would be really great to see some other filters like download count or star rating.
And, it’s really weird not seeing anything related to “run free”, which obviously is my search term, on the result page. Apparently, they need to tweak their search algorithm a bit too :)