This summer I planted pepper plants and noticed that these other plants have popped up after it has reached the end of its season. I think they are bell pepper plants but am unsure if they are since the original bell pepper plant died at the start of fall. Would appreciate some thoughts on if it is a bell pepper plant or not.
It's definitely a different kind of plant. Peppers have significant stems/branches and leaf stems. The leaves usually are not just growing all from one spot without branches (I mean, they don't grow like comfrey plants; they're more like trees in shape, even when young). They're usually (not always) a darker green color, too. I've never seen a bell type that wasn't a darker green color, actually, but it should easily be possible to breed one with light green foliage. Lower light and nutrient deficiencies could lighten the foliage, too.
You can see a bell pepper plant at this link, but if it happens to be broken some day, or if they remove the image, just do an image search for pepper foliage.
The plant does remind me of calendula (Bamboo mentioned that as a possibility in the comments already), and weeds I've seen before, but I don't know what it is.