If they all come from the same rootball you should be fine. It's quite possible that you just left a piece behind when you were moving it last fall and it's strong enough to put on a new growth. If you don't mind it there you could just leave it and watch it grow.

I'd gently remove some of the soil to see how they're attached and if they have individual roots. You can move the soil to the side of the roots and make a trench, then spray them with water to gently expose the roots and clean them off to have a good view. If there are individual roots growing I'd divide them but I'd wait until the fall when they're dormant. Since they're tree peonies they won't grow fast enough to be an issue before fall. They could've been from an eye of a root you accidentally left behind or could be seedlings, wouldn't be joined at all if that is the case.