Sounds reasonable, OP.
Of the 4 places I’ve had boarding experience in the past 10 years ago, 3 of which either asked for that liability coverage or strongly suggested it. They had neighboring farms where a horse got loose, damaged a car and/ or injured someone and the farm owner was pursued. I can’t recall but I think the horse owner was also pursued. They were just trying to protect themselves in every circumstance and each had their own farm policy.
Years ago a polo pony broke the tie line at ORHC. Horse galloped across the polo field, dragging the tie post between his hind legs, jumped the stone wall and landed on a car. Miraculously, horse escaped with only minor injury. And the car belonged to a groom returning from lunch. It was a beater, and the club didn’t cover his damages…
He was handy, had minimal insurance and just fixed it himself. So no lawyers involved but I’m sure it got people thinking…