Coriander (cilantro) is an annual, and a very short-lived one at that. In a warm or hot climate, its entire life-span can be as short as two weeks - which is why successive plantings are advised for a constant supply of leaves before it bolts.

I suggest the plants you see have germinated from dropped seeds from last year's plants. Such short-lived plants grow at a rate of knots!

Cilantros in my zone can overwinter like parsley, IFF they had benn planted in the fall not in the spring.
The spring planted ones will bolt, f.l.o.w.e.r and grow seeds.
Maybe in zone 6,where you are, they never bolt. They like real COOL weather, just like parsley.

Mine are still alive from last fall. If it's cool enough they will live. They bolt when it gets warm.

They are fun to see in the winter since they stay green under the snow unlike so many other things.

What I usually see is that late-planted/self-sown cilantro will survive the winter to die without bolting when the weather warms in the Spring. But whether they bolt or not, I would not expect much from them come spring. Expect to plant new cilantro.

FataMorgana

Cloverhouse, I have the same thing in my garden. Though the cilantro is matted down from the weight of 3 ft of snow for over a month. I really don't expect anything to come from them, but it will be interesting to watch.