Here in northern California we are overwhelmed with a giant Himalayan blackberry, the seed of which was imported by Luther Burbank around 1900. I spray several times every year as more come up. The birds eat the berries and spread the seed far and wide. Al

Hard to say from your description. Wild blackberries can branch naturally, but they would not end up looking like a "bush" with branches every few inches beginning near ground level. If you are hacking and yanking at them, excess branching could result. "Thicket" is the term used for an area of blackberry canes that have all grown together in a heap. This could look bushy from a distance.

Since you have been around these country blackberries a few years, I assume you noticed if they have blackberry-like blooms and fruit on them, unless you are keeping them weeded out before they have a chance to bloom.