There's some history behind it. The editor-in-chief, Y, and I are both participants in a mailing list devoted to Euclidean geometry. A few years ago, someone on-list proposed a problem, and several of us offered different ways of solving it. Y was apparently intrigued by my methods, and invited me to write a paper about the problem. I never got around to doing so, partly because of my own tendency to procrastinate, partly because I didn't really feel that I had enough of interest to say. I continued to think about the problem off and on, and eventually saw a way to generalize it quite a bit; the result was this paper. I think that Y may have been predisposed to accept this paper because of that history. (I did remind him of it in my cover letter.)

But I think the main reason for the fast turnaround is probably that it's an e-journal.