The number of photos taken using phones would no doubt dwarf the data used here, dedicated camera/lens combos are becoming something of a niche market, albeit still a sizeable one.
I use the Olympus EM-1, way down on the list. Nonetheless I found it interesting that the most commonly cited lenses used were the 12-40mm f/2.8, and the 40-150mm f/2.8. These are both excellent quality lenses, but relatively massive and quite expensive, at about $1000 and $1500 respectively.
Saying goes the merit of a photograph depends much more on the person using the camera than the camera being used.
It does in fact appear that the Canon 5D iii and the 6D are the two most common DSLRs on Flickr based on the number of photos posted. https://www.flickr.com/cameras/canon/
(The leading smartphones are still more popular in terms of total numbers.)
This. Of my friends, most people seem to have a bottom- or mid-range APS-size sensor DSLR from Canon or Nikon. But the two of my friends who actually have a 5D iii and a 6D, respectively, are the only ones who a) shoot photos that are interesting to people outside their immediate friends/family and who b) post those photos on flickr.
(While I'm the geek with the superzoom, or the '72 Nikon Nikkormat loaded with Tri-X when I'm feeling analog.)
(Also, chances are they'd skew the lens numbers significantly - while kit lenses come and go, pro glass tend to live much longer before being upgraded. (The 24-70mm f/2.8 which you often see around single-digit Nikon bodies, for instance, was the standard zoom for 8-9 years before being given an upgrade last year)
[ADDED: It actually appears that this does align with Flickr stats--which is, of course, not what you'd find on Facebook or other more mass market sites.]
My guess is that it's based on frequency. What is unknown is whether the sample takes more prolific photographers into account when calculating "common". 5000 people may all own same camera and take single public image as oppose to single photographer who takes 5000 images.
Very cool but would love more details on how they are defining their criteria.