HI miku,
It is very simple to identify the source of an article. you need to disable the sef url settings in the global config, as illustrated in the screenshot below :
http://easycaptures.com/fs/uploaded/551/3282067235.png
then you can refresh your frontend and check the url of the article :
Your_Site_URL/index.php?option=com_content&view=article&id=47&Itemid=500
Your_Site_URL/index.php?option=com_k2&view=item&id=32:beautiful-little-girl-blowing-dandelion&Itemid=294
there are many little tricks about joomla, i am sure, more you use it, more you shall learn about them.
Regards
Arvind