Google Manual Action Vs Remove URLs Request

Here is what happened to my site in chronological order with Images below.... 1, It got hacked and generated 50k spam pages with vigra links on it in the forum section. 2, I deleted the forum section (plugin) and cleaned the site. 3, I added "Remove URLs Request" in Google webmaster tools as shown below 4, I got the message as the URL's are removed successfully and you can see that page count in the index is low, The same can be verified by doing site:http://stockmarketoasis.com/, But there are still results showing 50k pages, but if you click next 100 pages you will see only 146.which confirms that the pages are removed. 6, Later after 1o days I get a mail in GWT that there has been manual action taken against my site for user generated spam pages. So my Question is....... Why there is a manual action even after i had put a remove url request. If I myself has requested a removed url request, then why there is a Manual action and what was the necessity. As per Google