Sort of. Smooth hydrangea (the Annabelle-like hydrangea, also called hydrangea arborescens) sometimes propagates from suckers like a Crape Myrtle. This makes the original single planting get wider and wider and wider... can be a pain sometimes.
I am curious how old and large this large hydrangea was. And if you took a picture of the root system that you found, would you mind posting a picture? Just curious so no problem if you did not take pics. Thanks in advance.