Here is a lesson I learned the hard way – if your compost is not hot enough, the seeds in it won’t die. I was thankful that the seeds which didn’t die turned out to be easy to see and pull.
The larger sprouts were from a gourd of some sort, pumpkin or squash more than likely. There are also more delicate looking seedlings in the mix, which sprouted in clumps. Those turned out to be tomato seeds from cherry tomatoes I had thrown out.
If I had more room, more time and more curiosity I would have let these grow to see what they produced. As it was, space was limited that year. My neighbor let some volunteers grow from their compost pile the following year and ended up with several different kinds of (decorative) pumpkins. If your plants are hybrids, their seeds will not be replicas of their parents, meaning you won’t know what they will be like. If that is what you are going for, then you will need to use heirloom seeds.