Of course, it would be natural to think it wasn't really Mark's bathroom. It could have been a bathroom that just happens to look the same. But according to this Tweet from Mark's roommate, it's definitely their bathroom.
In an interview with Buzzfeed, Jenna said she was at the party and, “When I went into the bathroom, I felt the need to take a mirror picture and posted it later.” So there's your explanation. And when you consider that Tinder matches you up with friends of friends, they mystery starts to make even more sense.
“I assumed that since we had a couple of parties before, it must have been from one of those nights,” Mark said to Buzzfeed. And with that, the mystery is solved. Although we still kind of wish she were actually some sort of selfie bandit.
Mark confirmed that messages between the two had indeed been sent. “I would be cool with meeting up with her,” Mark added. He also said that they had joked about “taking a picture together in the bathroom.”