Tumblr CEO meets Taylor Swift, wears T-Swift Tumblr meme shirt, meme evolves. It's the circle of life.
The prerequisite for understanding what happened here is extensive knowledge of the history of Taylor Swift memes. Are you qualified?
A brief recap: Once upon a time, there was a warning picture (above left) going around Tumblr of a girl supposedly named Becky who had died from snorting marijuana. People knew the picture was fake, because it's of Taylor Swift. Come on, fake drug PSA bloggers. Try a little harder.
Then, as a hilarious joke, Taylor Swift wore a shirt that said "no its becky." She never lets us down with her public photographs, that one.
Flash forward to present day. Tumblr CEO David Karp went to see a Taylor Swift concert, and he wore a "no its becky" shirt. He probably knew about the Tumblr meme from being the CEO of Tumblr, which requires him to read all blog posts. It's a hard job, but someone's got to do it.