I always have volunteers coming up everywhere. Kinda neat, but if the
seedling is from
seed from a hybrid cherry tomato
plant, then the chance of the fruit resembling it's parent are very slim and most times they taste terrible. Also, trying to grow tomato
plants indoors, especially indeterminate types, which this
seedling will most likely be, is very difficult and probably not worth the trouble. They need a great deal of light and a windowsill will not provide that. Sorry to be the bearer of bad news Amy, but it can't hurt to go ahead and try just for the experience.