The really suspicious thing is that over the last couple of months almost 1 Billion Tethers have been issued, which is highly suspicious because we wouldn't expect sane people to send such a gigantic amount of money to a shady Bitcoin exchange in the other end of the world, in exchange for a crypto token of dubious value. The most likely thing is that Bitfinex is using these unbacked Tethers that they are printing to purchase bitcoin in their exchange and push up the price.
It feels similar to the last bubble, which started out in MtGOX. MtGOX was insolvent (due to having a good chunck of their deposits lost to hackers and fraud). Eventually, they stopped letting people withdraw their US dollars so the only option people had was to purchase bitcoin and withdraw that instead. This extra demand pushed up the price which attracted outside speculation (the bitcoin price was higher than average in MtGOX but also quickly rose elsewhere) and kept MtGOX afloat for a bit longer than it should (because new investors kept throwing money on the dying exchange to get into the action).
For more Bitfinex news, I would recommend following https://medium.com/@bitfinexed
The simple truth is, an increasing number of people are buying Bitcoin whether those holding on to the past like it or not.
The thing that is harder to explain is that if this theory is true we should expect that the price of Bitcoin in Bitfinex to be higher than in other exchanges. I suspect that what is happening is that the rising prices in Bitfinex are helping attract a new wave of speculation and/or price manipulation, which is what is pushing up the price elsewhere. (This is what happened in the MtGOX bubble)