That wouldn't have happened with, say, a rough collie.

Smoothies too. Having owned several intact smooth collies, I can say they tend to "hold em high and tight." Add a low tail carriage and the balls stay hidden.

Long ago I was at the local dog park with Fawkes when a new dog arrived - a bully x boxer -ish mixed dog with docked tail and balls hanging down practically near his hocks. Conversation turned to "how intact dogs should not be allowed at the dog park." I pointed out that Fawkes was intact which surprised many there. "Well Fawkes is different."

And it was true but not because of ball status. Fawkes was a friendly dog with appropriate social skills. The incoming intact Bully-cross was known for being a jerk (a physical player who liked to body slam and roll dogs and who seemed to get his jollies from provoking dogs to snap back ) and had an indulgent idiot owner who thought all the other dogs were the problem.

Anyway, preaching to the choir here, a dog's personality and social skills are independent of his ball status. I've heard about the idea that neutered dogs reacting aggressively to intact dogs but haven't seen it with my male collies - Dino, Pablo, Fawkes or Alfie. Collie boys tend to be mild mannered by nature so maybe that puts other dogs at ease.