As you can see here, your indexer is returning to much stuff.
15-10-20 21:08:26.3|Trace|HttpClient|Res: [GET] https://nzbndx.com/api?t=tvsearch&cat=5030,5040&extended=1&apikey=&offset=0&limit=100&q=Limitless&season=1&ep=5 : 200.OK (370 ms)
15-10-20 21:08:26.3|Trace|NewznabRssParser|Parsed: Limitless.S01E04.720p.HDTV.DD5.1.x264-NTb
Although your search string specifies “ep=5” it’s also giving you other episodes. Try tweaking the search URL manually to determine why this is happening.
The indexer is also indicating that they do support episode searching:
> <searching><search available="yes" supportedParams="q"/>
> <tv-search available="yes" supportedParams="q,rid,tvdbid,tvmazeid,season,ep"/>
> <movie-search available="no" supportedParams="q"/>