There are morning-and-caffeine writers, and there are nighttime-and-alcohol writers. You pick the time of day when your brain feels best, and pick the substance that brings it out.
I thought that was a quote from a writer, but I think I just wrote it in my journal once. Maybe I was inspired by an interview or article that gestured toward the distinction. This was during a phase where I found myself transitioning from a morning-and-caffeine writer to a nighttime-and-alcohol writer (a frightening change, for the record).
I do my best writing once or twice a year while flying. There is something about big, public space designed for transience; the intimacy of families or couples traveling together in massive crowds; the convergence of languages and accents.
Most likely, airports are just ideal spaces for people watching, which is the third most important writerly activity (the second most important is sitting and staring into space, and the first most important is writing/typing sentences). Everybody is too concerned with their own journey to look up, so a person with a long layover gets the best view—especially if you happen to be in the Charlotte airport, where the main terminal is lined with rocking chairs.