I am not sure how you are creating the feed to Joomla articles? (there are several methods). RT no longer produces anything specific to K2 at all. You might be better to enquire on the K2 forums.
Please search forums before posting. Please make sure your post includes the version of the CMS you are using and a link to the problem. Annotations on screenshots can also be helpful to explain problems/goals. Please use the "secure" tab for confidential information.