Not sure if you looked at your Traffic Sources of the My Account Page or not. There is a link at the top of the page. There you will see your overall traffic sources. For instance HP, Google, Google[au] for Google Australia, Bing, Pinterest, individual Hubbers, facebook, website domains, and etc.
For instance once I had a Hub on Aspartame that received a giant leap in traffic (For me similar to yours) and it arrived from one particular Website. It was posted in one of the forums.
Remember social sharing is not backlinking. The URL is posted and shared bringing views. For instance the link shared at that site for a Forum post is a backlink, but it is only one. Anyway, there may be a big boost in traffic if someone tweets at Twitter, pins at Pinterest, or shares at Facebook. Some of my Poems get mediocre traffic from Facebook with short surges.
The only way I know how to find out if your Hub has inbound links is with a tool bar or analyzer provided by a website. Some examples are Moz.com , SEMrush Intelligence, Majestic or others. Usually they are a subscription service, but some provide a free trial service.