GoodROI and lucy both got it right.
A robot.txt doesn't prevent a page from showing up in the SERP, it only prevents it from being crawled. If that page is linked to from enough outside sources the URL will still show in a SERP, but without any additional information (meta description etc.)
A meta no-index tag is on the specific page and prevents that page from showing in the SERP altogether... the only catch is the page has to be crawled for the crawler to find the meta no-index tag.
So take that page off your robots.txt is the moral of the story