Most of the "worlds most expensive" photographs are almost always sold at auction, where there is a clear record of the transaction. Auctions might not actually disclose who the buyer was, but the sale can be confirmed. This "press release" from Lik claiming to have made and sold 4 of the worlds most expensive photographs to some 'undisclosed' private collector seems to be more hype than self-promotion.
The guardian article, using this press release to bash photography as an art makes the old tired (and wrong) comment on the ubiquity of cameras and photographs and how it can never be art. The Forbes article is a much better comment about the long term "value" of an artist and how the work is valued in the secondary market ( http://www.forbes.com/sites/kathryntully/2014/12/12/is-this-the-worlds-most-expensive-photograph/ ).
If this is true, I think the buyer should have waited a few days and put that 6.5 mil to get some real masterworks: http://www.sothebys.com/en/auctions/2014/175-masterworks-n09275.html
Richard Boutwell