Wait, Sinterklaas has a witch horse? How does that work?

Like, does the horse cast spells or curse people? Does it wear a pointy black hat? Does Sinterklaas ride a horse that, in turn, rides a broom?

Or is it a horse he adopted after a witch didn’t want it anymore? If so, what did the witch need a horse for when she had the broom? As a pack animal? For companionship? To disguise the fact that she’s a witch while traveling above walking speed?