Mysterious Stroller-Leaver(s)

Eating lunch

So the other day we found what appears to be a brand new double jogging stroller on the landing below ours (in between two levels, so not outside anyone's door), with the user's manual. For some reason my first thought was, "Someone's moving in with twins!!" because we have an empty unit below us. Silly me. It's clear now that it was for us, but we still do not know who did it. I have an idea...but I'm befuddled at the anonymity. The boys have taken to it. They insisted on eating lunch in it yesterday and after their nap they watched a movie in it, drinking their milk and eating their veggie straws. Why does the stroller-leaver wish to remain a mystery? Any ideas? Is said person reading this blog and chuckling right now?