MontyJ
Deeply Rooted
It's probably a volunteer tomato plant. When you look at the odds, a seed from a potato plant, dropped from a bird, actually germinating in the garden are pretty small. The appearance resembling a potato plant could easily be explained by the growth habit of a tomato growing under cooler than normal conditions. Check the stems and undersides of the leaves for a purple color. Posting a pic would also definately help.