You have in fact already given the answer yourself 
Data in text/image columns is, from a space accounting point of view, seen as an 'index', even though it actually is not an index. This could well explain why you're seeing those numbers.
To get confirmation, run "sp_spaceused REPOSITORY_SPACE, 1", which will list the space used per 'index'. Text/image data is displayed as an index named "t" followed by the table name, so in your case I would expect it to be named "tREPOSITORY_SPACE".