A link that is labeled "no follow" means that an coding attribute had been coded into the HTML code which constructs that link. The effect of which is that search engine will not use that link in it overall scheme/algorithm for determining the search engine rankings of the pages in its search results.
It is a bit technical. If you are not into SEO (search engine optimization) and web search engine algorithm and if you do not code HTML, you don't need to worry about it too much.
It do not have anything to do with weather the Hub is good or bad, and it is not a penalty or anything like that. It does not affect your Hub article score or anything else.
Basically, whether it is "no follow" or not doesn't have much consequences -- unless you are and SEO consultant or web developer trying to game or equalize the system in page ranks, etc.