Honestly, I think that most "leaks" are intentional. That's how they maintain the hype and test the waters before they're ready to officially reveal anything. Assuming this is legit, anyone who was trusted with one of these phones, and probably had to sign a s**t-load of papers about confidentiality and whatnot, probably isn't dumb enough to take a selfie with it and post it on Instagram.
People see "BREAKING NEWS: iPhone 7 leaked" followed by more leaks and specs and whatnot. You'll get people asking "I wonder what it'll do/how's the camera gonna work/ect" It'll get more discussion going for the 7. Stuff like that is nothing but marketing to help draw up hype for the iPhone. Apple, and other companies for that matter, have pulled this stuff for years. iPhone 7 is already shaping up to be the most controversial smartphone apple has ever produced and it's not even even out yet. And like 80% of the people who are like "I ain't getting the new iPhone" will end up buying one. Like said its all marketing, with a bit of human psychology thrown into it.
Tbh, it would be the coolest thing ever if all the 2017 iPhone specs were really for the 7. Doubt that would happen but it would be hella cool if it did...and it would be the ultimate plot twist in this iPhone saga