Thanks for the reply Sandeep! I have edited the post and have submitted for the approval.
I would like to say that, firstly my colleague did not add any code for downloading the source code. He just uploaded the code in the right hand panel of the web page. Secondly, he does not even know about this css class called "download". Still, the same download widget appears on his web page.
I also faced issues in uploading the code snippet which I have discussed in another Thread. Uploading complete class is not an issue, but when we think of attaching just code snippet, then we need to format it manually with the pre block.
What I asked was how to fix it. All that would happened by default if you would have used the article submit workflow where it asks if any download to be attached.
About code blocks, you need to always wrap it with a pre tag with a defined language to get proper colorization. You don't need to know any class or style. Put few line of code, select them and use 'code -> C#' for C# code lines. It will automatically apply the need HTML with attribute if any.
Since, I could not edit your article, I suggested you a way to do it yourself.