I thought it was a Pepper plant

I didn't plant any tomatoes. I planted sweet red bell peppers. I saved the seeds from some peppers that we ate. This is what grew from the seeds. I've been watching this 'fruit' develop, thinking to myself, gee, this looks like a tomato. I thought that maybe it was a stunted red pepper because I didn't buy seeds and instead used them from a store-bought pepper. It just didn't get any bigger, and then suddenly it turned nice and red. So I took some pictures of it, picked it, and sliced it open. It was a very delicious cherry tomato. I'm stumped. No, I didn't use any compost in my garden. I did re-use the dirt from my old garden, but I let that garden sit fallow for two years before moving the bed to its present location. Yes, I grew yellow pear tomatoes in the old garden. Yellow Pear, not Cherry.