The Magic of Nature

So each year I plant some tomato seeds and get a little crop of scraggly plants that provide my meager existence with some produce. This year I didn't do any planting on my own, but let nature do its thing by just letting what ever came up out of the ground take root; survival of the fittest, the heartiest (or is it hardiest? can never remember) plant wins. So imagine my surprise when a few weeks back I notice, these are not cherry tomatoes which I've planted for the last 2-3 years but Roma tomatoes which I planted back in another apartment, in another part of town, at least 3 years ago. (and very unsuccessfully at that, I got maybe 2 or 3 tomatoes off the plant and they weren't very good at that) Where did they come from? These seem very hearty (or hardy again); there's about 20 or 30 of them on the vine right now. Seem to be taking their time ripening though!