OK I just watched this On Demand (it's Episode 6).
And when the roll over so that Somerhalder is on his back, you can see his dick. It is not inside her and looks to be semi hard. It is sort of floppy, and looks to be a modest but solid 6 to 7 inches. I believe it is what you see in the second image above. Timecode in the video above is around 1:52.
Although the director says it's simulated sex (which I believe), it is certainly not similar body parts. That's his ass, those are her tits, and I am pretty sure that's his dick.