The robots.txt disallow is fighting the robots meta tag noindex. By disallowing all (well behaved) bots, you're preventing the engines from seeing the noindex robots meta.
Unless Google sees the noindex robots meta, it will do its best to index "good references" it can find to a page, even if it hasn't crawled the page. So, if there are active links out there still pointing to your page, Google will index the url in the link, and it will sometimes rank it.
Does this look like it might be text in any way related to your page, as in a link anchor that might have been linking to you?
[edited by: Robert_Charlton at 10:06 am (utc) on Jan. 27, 2008]