Do the Brackens, like the Ryswells, breed horses or is their sigil related to something else

According to the Blackwoods:

“It goes back to the Age of Heroes. The Blackwoods were kings in those days. The Brackens were petty lords, renowned for breeding horses. Rather than pay their king his just due, they used the gold their horses brought them to hire swords and cast him down.”

The Brackens disagree.