This is growing where I planted some pepper seads this spring. Using the various weed identification sites, the closest thing I can to is Swamp Smartweed. Also know as water pepper. It should be some sort of pepper, but it's not doing much but growing and has these seed pods/clusters. So far no flower. It appears to have ochrea at each branch. (each leave is one leaf off the main branch.)
The leaves are distinctly bi-colored with a dark and light green on them. Almost looks like shadows, but it's not.
Yes, those are the flowers and it is a Persicaria of some sort. Even if it is one of the Persicaria's with "pepper" as part of the common name, it is not a real pepper and is not at all related to the peppers you planted and were expecting to come up there.
what you are calling seeds on the picture are flower heads, not seeds, but possibly in the early seed-forming stage. flowers have to come before the seeds, not after. even though it flowers, it's still a weed.
hope this makes it more clear for you.